Lymphoma / Lymphosarcoma

Lymphoma, also known as lymphosarcoma, represents a malignant neoplasm arising from lymphoid tissue that affects multiple farm animal species including cattle, sheep, goats, pigs, and poultry. This cancer originates from lymphocytes, the white blood cells responsible for immune function, and can develop in lymph nodes, spleen, bone marrow, and virtually any organ containing lymphoid tissue. In cattle, lymphoma represents the most commonly diagnosed malignant tumor and carries significant economic importance due to carcass condemnation at slaughter and premature loss of productive animals. The disease manifests through various clinical presentations depending on which anatomical form develops and which organs become infiltrated with neoplastic lymphocytes.

Cattle lymphoma occurs in two distinct epidemiological patterns that differ in cause, age distribution, and geographic prevalence. Enzootic bovine leukosis, caused by bovine leukemia virus infection, represents the predominant form in many cattle populations worldwide and typically affects adult animals over three years of age. Sporadic bovine leukosis occurs independently of viral infection and includes juvenile, thymic, and cutaneous forms affecting younger cattle. In small ruminants, lymphoma occurs sporadically without known viral association in most cases. Porcine lymphoma is relatively uncommon but recognized, while poultry lymphoma has important associations with viral infections including Marek's disease virus and avian leukosis virus.

The economic and welfare impact of lymphoma in farm animals is substantial, particularly in cattle operations where the disease causes significant losses. Carcass condemnation at slaughter represents immediate economic loss, with any evidence of lymphoma requiring rejection for human consumption in most regulatory jurisdictions. Premature culling of affected animals eliminates future production potential and genetic contribution to the herd. Reduced productivity often precedes overt clinical disease, causing subclinical economic losses. Animal welfare concerns arise from the progressive nature of the disease and the suffering associated with advanced malignancy. In cattle, BLV control programs aim to reduce these losses through testing and management strategies.

Early detection of lymphoma is challenging because initial stages often produce subtle or nonspecific clinical signs, and many affected animals remain subclinical until disease progression is advanced. Diagnosis typically occurs during clinical examination revealing lymph node enlargement, at slaughter inspection, or through diagnostic workup for nonspecific illness. Treatment options for lymphoma in food-producing animals are extremely limited due to economic constraints, withdrawal time concerns, and the generally poor prognosis associated with malignant lymphoid neoplasia. Management focuses primarily on prevention through BLV control, early identification of affected animals, and appropriate culling decisions to minimize losses and prevent viral transmission in endemic herds.

The causes of lymphoma in farm animals vary significantly between species and disease forms, ranging from viral infection to sporadic neoplastic transformation of unknown etiology. In cattle, bovine leukemia virus represents the causative agent for enzootic bovine leukosis, the most common form of cattle lymphoma in endemic regions. BLV is a retrovirus that infects B lymphocytes and integrates into the host cell genome, where it can persist for life and occasionally trigger malignant transformation. Only a small percentage of BLV-infected cattle, estimated at one to five percent, ultimately develop lymphoma, but infection precedes tumor development by several years. Sporadic bovine leukosis occurs without BLV involvement through mechanisms that remain incompletely understood.

Genetic predisposition influences lymphoma development, particularly regarding susceptibility to BLV infection and subsequent tumor formation in cattle. Certain major histocompatibility complex haplotypes have been associated with resistance or susceptibility to persistent BLV infection. Animals with specific genetic backgrounds may be more likely to develop lymphoma following BLV infection, while others maintain persistent infection without progressing to malignancy. Breed influences remain difficult to separate from management and exposure factors, though dairy cattle appear disproportionately affected, possibly reflecting longer lifespans, intensive management, and higher BLV prevalence in dairy versus beef operations.

Environmental and management factors significantly influence BLV transmission within cattle herds, indirectly affecting lymphoma incidence. The virus spreads through transfer of infected lymphocytes between animals, occurring via contaminated needles, dehorning equipment, rectal examination sleeves, and other blood-contaminated fomites. Natural transmission through direct contact is less efficient but contributes to spread in closely confined groups. Colostrum and milk can transmit infection to calves, though this route is less important than iatrogenic transmission. Intensive dairy management with frequent animal handling and shared equipment creates numerous transmission opportunities. Insects capable of mechanical transmission may contribute to spread in some environments.

Risk factors for lymphoma development include BLV infection status, age, immunological factors, and potentially concurrent diseases. In BLV-infected cattle, advancing age substantially increases lymphoma risk, with most cases occurring in animals over four to eight years old. Immunosuppression from any cause may increase probability of neoplastic transformation in infected animals. High proviral load, indicating extensive viral integration into the genome, correlates with increased lymphoma risk. Co-infection with other pathogens and chronic stress may influence immune surveillance and tumor development. For sporadic forms, specific risk factors remain largely unidentified.

The pathophysiology of lymphoma involves progressive accumulation of neoplastic lymphocytes that infiltrate and eventually replace normal tissue architecture in affected organs. In BLV-associated disease, viral proteins interfere with normal cell cycle regulation and apoptosis, allowing infected cells to accumulate and occasionally undergo additional genetic changes leading to malignancy. Tumor cells proliferate within lymph nodes causing enlargement, and spread through lymphatic channels and blood to infiltrate multiple organs including liver, spleen, heart, kidneys, abomasum, uterus, spinal canal, and virtually any tissue. Progressive organ infiltration eventually impairs function, producing clinical signs related to the organs most severely affected. Terminal stages involve widespread tumor burden, metabolic derangement, and organ failure.

Early warning signs of lymphoma in farm animals are often subtle, nonspecific, or entirely absent, making early detection challenging in production settings. Initial manifestations may include mild weight loss, decreased appetite, reduced milk production in dairy cattle, or subtle changes in behavior that are easily attributed to other causes. Some animals develop visible lymph node enlargement before other signs become apparent, providing an opportunity for early detection through careful observation and palpation. Subclinical disease may be suspected when BLV-positive animals show declining condition without other explanation. Astute producers and veterinarians may recognize a pattern of vague illness in adult cattle that precedes definitive lymphoma diagnosis.

Clinical presentation varies considerably between species and depends heavily on which organs are affected by tumor infiltration. In cattle, several distinct anatomical forms are recognized, each producing characteristic clinical syndromes. Multicentric lymphoma affecting multiple lymph node groups represents the most common form and causes generalized lymphadenopathy with symmetric enlargement of peripheral and internal nodes. Digestive tract lymphoma with abomasal involvement causes weight loss, decreased appetite, and potentially melena from gastrointestinal bleeding. Cardiac lymphoma affecting the heart and surrounding structures produces signs of cardiac dysfunction including jugular distension, ventral edema, and muffled heart sounds. Spinal lymphoma causes progressive posterior paresis or paralysis through tumor compression of the spinal cord.

Behavioral changes in animals with lymphoma reflect general malaise, discomfort from tumor masses, or specific organ dysfunction. Affected animals often separate from the herd and show decreased interest in feeding and social interaction. Reduced rumination and cud chewing may be observed in ruminants. Lethargy and weakness progress as disease advances. Animals with painful tumors or organ involvement may show abnormal postures or reluctance to move. Behavioral changes may precede more obvious physical findings by days to weeks, though some animals maintain relatively normal behavior until advanced disease stages.

Physical signs detectable on examination provide the most definitive clinical evidence of lymphoma. Palpable lymph node enlargement affecting superficial nodes including prescapular, prefemoral, mandibular, and superficial cervical nodes represents a cardinal finding. Affected nodes are typically firm, non-painful, and may be dramatically enlarged. Internal lymph node enlargement may be detected through rectal palpation of iliac nodes in cattle. Exophthalmos may occur with retrobulbar tumor development. Skin involvement produces nodular or diffuse thickening, particularly in cutaneous lymphoma forms. Body condition typically declines progressively, and affected animals appear unthrifty despite adequate nutrition.

Symptom progression in lymphoma follows a generally predictable pattern of gradual worsening over weeks to months, though the rate of decline varies considerably between individuals. Initial localized disease often progresses to involve multiple organ systems. Weight loss accelerates as metabolic demands of tumor growth exceed nutritional intake. Organ-specific dysfunction becomes more apparent as tumor burden increases. Anemia may develop from bone marrow involvement or chronic disease effects. Respiratory signs emerge if thoracic lymph nodes enlarge to compress airways. Terminal stages involve cachexia, weakness, recumbency, and death from organ failure or secondary complications.

Emergency symptoms requiring immediate veterinary intervention include signs of acute organ dysfunction or rapidly progressive disease. Sudden posterior paralysis from spinal cord compression requires urgent evaluation, though prognosis is poor regardless of intervention. Acute respiratory distress from airway compression or pleural effusion constitutes an emergency. Profound weakness, recumbency, and inability to rise indicate advanced disease requiring immediate assessment. Severe bleeding from gastrointestinal tumors may cause acute collapse. Any sudden deterioration in a lymphoma suspect warrants emergency evaluation to determine whether intervention is appropriate or humane euthanasia should be considered.

Clinical examination provides initial evidence supporting lymphoma diagnosis, with certain findings highly suggestive of the condition. Systematic palpation of all accessible lymph nodes documents enlargement, asymmetry, and node characteristics. Normal lymph nodes are typically small, soft, and mobile, while neoplastic nodes are enlarged, firm, and often fixed to surrounding tissues. Rectal examination in cattle allows palpation of internal iliac lymph nodes, which are frequently affected in lymphoma cases. Complete physical examination assesses body condition, identifies potential sites of organ involvement, and rules out alternative diagnoses. Auscultation may reveal cardiac abnormalities associated with cardiac lymphoma including muffled heart sounds and arrhythmias.

Diagnostic testing confirms lymphoma diagnosis and may provide information about extent and prognosis. Complete blood count and serum chemistry panels assess overall health status and may reveal abnormalities including anemia, abnormal lymphocyte numbers, hypercalcemia, or organ-specific changes. BLV serology testing determines infection status in cattle and confirms viral association when positive in animals with lymphoma. Cytological examination of fine needle aspirates from enlarged lymph nodes can demonstrate neoplastic lymphocyte populations, though interpretation requires expertise. Biopsy with histopathological examination provides definitive diagnosis by demonstrating tissue architecture disruption and neoplastic lymphoid cell populations.

Differential diagnosis for lymph node enlargement and suspected lymphoma includes numerous conditions requiring systematic evaluation. Lymph node hyperplasia from chronic infection or inflammation causes generalized or regional lymphadenopathy that must be distinguished from neoplasia. Abscesses and other localized infections may cause node enlargement with different characteristics. Caseous lymphadenitis in sheep and goats produces lymph node enlargement that may mimic lymphoma. Other neoplasms rarely cause lymph node enlargement in farm animals. Tuberculosis and paratuberculosis may cause lymph node changes, though with different characteristics. Thorough evaluation including appropriate testing differentiates these conditions from lymphoma.

Herd-level diagnostics apply primarily to BLV-associated lymphoma in cattle, where testing programs support control efforts. Serological screening using ELISA testing identifies BLV-infected animals within herds, informing management decisions. Bulk tank milk testing provides cost-effective screening for dairy herd infection status. Polymerase chain reaction testing can identify infected animals and quantify proviral load. Herd prevalence determination guides decisions about control program intensity and economic feasibility. Slaughter surveillance and carcass inspection data provide information about lymphoma frequency and economic impact. Necropsy examination of animals dying or culled with suspected lymphoma confirms diagnosis and characterizes disease distribution.

Emergency treatment for acute lymphoma complications focuses on animal comfort and immediate stabilization while longer-term management decisions are considered. Respiratory distress from airway compression may be partially relieved through positioning and administration of anti-inflammatory medications, though underlying tumor burden remains. Severe anemia may warrant blood transfusion in valuable animals if this aligns with overall treatment goals. Pain management using appropriate analgesics improves quality of life for animals with painful tumor masses or organ involvement. In most cases, emergency presentation of lymphoma indicates advanced disease where humane euthanasia may represent the most appropriate response.

Medical management options for lymphoma in food-producing animals are severely limited compared to companion animal and human oncology. Chemotherapy protocols used in dogs and humans are generally not applicable to food-producing animals due to drug withdrawal concerns, expense relative to animal value, and regulatory restrictions on administering certain medications to animals entering the food supply. Corticosteroids may provide temporary improvement through lymphocyte suppression and anti-inflammatory effects but do not represent curative therapy. Any medications administered to food-producing animals must observe appropriate withdrawal periods, and animals treated with many chemotherapy agents cannot enter the food chain. The practical reality is that medical treatment rarely represents a viable option for lymphoma in farm animals.

Surgical intervention plays minimal role in lymphoma management given the systemic nature of the disease. Unlike localized tumors amenable to excision, lymphoma represents a systemic malignancy affecting multiple sites simultaneously or sequentially. Surgical biopsy may be performed to confirm diagnosis but does not constitute treatment. Removal of visibly enlarged lymph nodes would not address disease at other sites. In rare cases of truly localized presentation, surgical excision might be considered, but lymphoma in farm animals is almost invariably systemic by the time of diagnosis. Surgery plays no meaningful role in lymphoma treatment for food-producing animals.

Supportive care represents the primary management approach for animals where immediate culling is not elected, focusing on maintaining comfort and quality of life during disease progression. Provision of easily accessible, high-quality feed supports nutritional status despite reduced appetite. Fresh water availability and comfortable housing reduce additional stressors. Separation from aggressive herdmates prevents injury to weakened animals. Monitoring for disease progression guides decisions about when intervention is no longer appropriate. The goal of supportive care is maintaining acceptable quality of life for a defined period rather than achieving cure or long-term remission.

Herd treatment protocols do not apply to lymphoma management per se, but herd-level approaches to BLV control reduce future lymphoma incidence. Testing and segregation programs separate BLV-positive from negative animals to reduce transmission. Cull-positive programs systematically remove infected animals to eliminate the virus from herds. Test-and-management approaches maintain infected animals while implementing measures to prevent new infections. Single-use needle policies and instrument disinfection between animals reduce iatrogenic transmission. Control program selection depends on herd prevalence, economic factors, and producer goals.

Treatment decisions for lymphoma ultimately center on economic and welfare considerations that typically favor early culling over prolonged management attempts. The poor prognosis associated with lymphoma means that treatment investment rarely provides positive return. Animal welfare considerations argue against prolonging the life of animals with progressive, incurable malignancy beyond the point of acceptable quality of life. Carcass condemnation occurs regardless of disease stage at slaughter, so earlier culling may salvage hide and non-edible byproduct value. BLV-positive animals with lymphoma represent ongoing transmission risk and removing them protects herd health. For most animals diagnosed with lymphoma, prompt humane culling represents the most appropriate management decision.

Recovery from lymphoma in the conventional sense of cure and return to normal health does not occur in farm animals with this malignancy. Lymphoma in livestock represents a progressive, fatal disease for which no curative treatments are available or economically justified. Animals diagnosed with lymphoma will succumb to the disease, typically within weeks to months of clinical diagnosis, depending on disease form, extent, and individual factors. The term recovery is therefore not applicable to lymphoma in the way it applies to treatable conditions. Discussion instead focuses on disease timeline, managing the terminal period, and factors affecting survival duration.

Post-diagnosis care and monitoring for animals not immediately culled involves tracking disease progression and maintaining quality of life. Regular assessment documents changes in tumor burden, body condition, appetite, and behavior. Specific monitoring depends on the anatomical form present, such as watching for respiratory signs in animals with thoracic involvement or neurological changes in those with spinal cord compression. The goal of monitoring is identifying the appropriate time for euthanasia rather than tracking improvement. Caregivers must be prepared for the reality that decline rather than improvement will occur.

Prognosis factors influencing survival time include the anatomical form of lymphoma, extent of organ involvement, tumor growth rate, and overall animal condition at diagnosis. Animals with slowly progressive disease may survive several months while those with aggressive tumors or critical organ involvement may decline within days to weeks. Cardiac and spinal forms often progress rapidly once clinical signs appear. Multicentric forms with massive lymphadenopathy may follow variable courses. Younger animals with sporadic forms sometimes survive longer than older cattle with BLV-associated disease. However, all forms are ultimately fatal, and survival time differences are measured in weeks to months rather than years.

Return to production is not a realistic goal for animals diagnosed with lymphoma. Affected dairy cattle cannot resume normal milk production, and maintaining them in the milking herd creates labor demands, contamination risk from possible tumor rupture, and ongoing BLV transmission opportunity. Beef animals with lymphoma are condemned at slaughter regardless of clinical status, so continued feeding provides no return. Breeding animals with lymphoma should not be used for reproduction given disease progression and potential genetic transmission of susceptibility factors. The appropriate decision point for most lymphoma cases is when diagnosis is confirmed rather than after attempting a futile recovery period.

Vaccination protocols for lymphoma prevention are limited, though BLV vaccine development has been an area of research interest. Currently, no commercially available vaccines effectively prevent BLV infection in cattle, though experimental vaccines have shown some promise. Unlike Marek's disease in poultry where effective vaccination dramatically reduces tumor incidence, no equivalent option exists for bovine lymphoma. Prevention therefore relies on management practices to reduce transmission rather than immunological protection. Future vaccine development may eventually provide additional prevention tools, but current control programs must focus on non-immunological approaches.

Biosecurity measures form the cornerstone of BLV prevention and consequently reduce lymphoma incidence in cattle herds. Preventing introduction of infected animals through testing and quarantine of new additions represents the first line of defense. Source herd BLV status should be determined before purchase, with preference for test-negative herds. Closed herd management eliminates introduction risk entirely where feasible. Internal biosecurity preventing transmission between infected and susceptible animals within a herd reduces new infection rates even when elimination is not immediately achieved. Visitor and equipment policies should address potential external contamination sources.

Prevention through management practices addresses the primary transmission routes for BLV. Single-use needles for all injections eliminate the most efficient transmission mechanism. Disposable rectal sleeves changed between animals prevent transmission during reproductive procedures. Dehorning and other surgical equipment should be disinfected between animals or individual instruments used. Tattooing, ear tagging, and other procedures breaking skin should use disinfected equipment. Colostrum management including heat treatment or use of colostrum from test-negative dams reduces calf infection. Natural service breeding avoids transmission that can occur through AI equipment, though bulls should be tested.

Management practices beyond direct transmission prevention support overall herd health and BLV control program success. Testing programs identify infected animals, enabling informed management decisions. Segregation of positive and negative animals into separate groups reduces transmission opportunity. Fly control may reduce potential mechanical transmission by biting insects. Record keeping tracks test results, infection dates, and lymphoma cases for program evaluation. Regular herd testing monitors infection trends and control program effectiveness. Economic analysis guides decisions about control program intensity and culling thresholds.

Quarantine and testing protocols provide structured approaches to BLV control with varying intensity based on herd goals and circumstances. All new herd additions should be tested before introduction, with positive animals rejected or quarantined. Test-and-cull programs remove all positive animals, achieving elimination when consistently applied but requiring significant initial culling in high-prevalence herds. Test-and-segregate approaches maintain positive and negative groups separately, preventing new infections while retaining productive infected animals. Whole-herd testing at regular intervals monitors infection status and identifies new infections. Testing should use validated serological methods with appropriate sensitivity and specificity for the program goals.

Daily management and monitoring of animals diagnosed with lymphoma focuses on welfare assessment and appropriate culling decisions rather than maintaining long-term productivity. Daily observation notes appetite, water intake, behavior, and ability to rise and move normally. Progressive weight loss and declining condition are expected and should be monitored objectively. Pain assessment guides decisions about analgesic use and culling timing. Animals should be evaluated for their ability to maintain acceptable quality of life, with clear criteria established for when this is no longer achieved. The goal is preventing unnecessary suffering while avoiding premature culling if the animal maintains reasonable comfort.

Housing and environmental management for animals with lymphoma should prioritize comfort and ease of care. Affected animals may need separation from the main herd to prevent injury from dominant herdmates and allow individual monitoring. Housing should provide comfortable resting areas with adequate bedding. Easy access to feed and water accommodates weakened animals. Protection from extreme temperatures reduces additional physiological stress. Facilities should allow efficient handling for assessment and treatment administration while minimizing animal stress. Non-slip flooring prevents injury in animals with progressive weakness.

Herd health programs addressing lymphoma focus primarily on BLV control to prevent future cases rather than managing affected individuals. Establishing herd BLV prevalence through testing provides baseline data for control program design. Program goals should be defined based on prevalence, economic factors, and producer commitment. Implementation plans specify testing frequency, management of positive animals, and biosecurity measures. Regular program evaluation assesses progress toward goals and identifies areas for improvement. Veterinary involvement ensures appropriate testing methods and interpretation of results.

Record keeping systems support both individual animal management and herd-level control programs. Individual records document diagnosis date, clinical findings, treatments administered, and eventual outcome. Herd records track BLV test results, new infections, and lymphoma cases over time. Analysis of herd data identifies risk factors and evaluates control program effectiveness. Slaughter records provide valuable information when available. Compliance documentation demonstrates adherence to control program protocols. Records support economic analysis of disease impact and control program costs and benefits.

Economic considerations for lymphoma management encompass direct losses, control program costs, and market implications. Direct losses include carcass condemnation, premature culling, and reduced productivity. BLV control programs involve testing costs, potential culling losses, and management changes. Economic analysis should compare control program costs against ongoing losses from endemic infection. Market access considerations may influence control decisions, as some export markets and premium programs require BLV-negative status. Insurance coverage for lymphoma losses varies and should be understood. Long-term economic benefits of BLV control include reduced lymphoma incidence, potential market advantages, and improved overall herd health.

Breed susceptibility to lymphoma varies based on BLV infection rates and genetic factors influencing disease progression following infection. Dairy breeds appear disproportionately affected by lymphoma compared to beef breeds, though this largely reflects higher BLV prevalence in dairy herds rather than intrinsic breed susceptibility. Holstein cattle show high lymphoma rates in endemic areas, correlating with high BLV prevalence and intensive management practices that favor transmission. Jersey, Guernsey, and other dairy breeds have similar susceptibility when maintained under similar conditions. Dairy cattle's longer productive lifespans provide more time for tumor development following infection, as lymphoma typically appears years after initial BLV exposure.

Production type significantly influences lymphoma risk through effects on BLV prevalence and age at culling. Dairy operations with frequent animal handling, shared equipment, and older animal demographics create conditions favoring both BLV transmission and lymphoma development. Beef cattle in extensive systems have lower BLV prevalence and are typically marketed before reaching ages when lymphoma commonly develops. Feedlot cattle rarely develop clinical lymphoma despite sometimes originating from BLV-positive herds, simply because they do not live long enough. Breeding beef herds maintaining animals to older ages have intermediate risk. Dual-purpose operations may have risk profiles between intensive dairy and extensive beef depending on management practices.

Genetic selection and testing approaches for lymphoma reduction focus on BLV resistance rather than direct lymphoma susceptibility. Research has identified major histocompatibility complex alleles associated with resistance to persistent BLV infection. Animals with certain BoLA genotypes clear infection or maintain low proviral loads that may reduce lymphoma risk. Genetic testing for these markers could theoretically support selection programs, though commercial application remains limited. Selecting for these resistance alleles while maintaining other important production traits requires balanced breeding goals. Future genetic tools may enable more effective selection for BLV resistance, reducing lymphoma incidence through reduced infection prevalence and possibly reduced tumor development risk in infected animals.

Commonly co-occurring conditions with lymphoma reflect both direct disease effects and consequences of progressive malignancy. BLV infection itself, while causing clinical disease in only a minority of infected cattle, may reduce immune function and increase susceptibility to other infections. Animals with lymphoma frequently develop secondary infections due to impaired immune surveillance. Anemia commonly accompanies lymphoma, resulting from bone marrow infiltration, chronic disease effects, or blood loss from gastrointestinal tumors. Hypercalcemia occurs in some lymphoma cases and causes additional clinical problems. Cachexia and muscle wasting develop as metabolic demands of tumor growth exceed nutritional intake.

Conditions with similar presentation to lymphoma must be differentiated through appropriate diagnostic evaluation. Generalized lymph node enlargement may result from chronic infection, inflammatory conditions, or reactive hyperplasia rather than neoplasia. Caseous lymphadenitis in sheep and goats causes lymph node enlargement with abscess formation. Tuberculosis and paratuberculosis can cause lymph node changes in cattle. Actinobacillosis and actinomycosis may produce localized swellings mimicking lymph node enlargement. Heart failure from causes other than cardiac lymphoma produces similar clinical signs including jugular distension and ventral edema. Spinal cord compression from vertebral abscess or trauma mimics spinal lymphoma presentation.

Complications and sequelae of lymphoma relate to organ dysfunction from tumor infiltration and general effects of progressive malignancy. Cardiac involvement leads to congestive heart failure with pleural and pericardial effusion. Spinal cord compression causes irreversible paralysis as tumor destroys neural tissue. Gastrointestinal infiltration leads to malabsorption, weight loss, and potentially fatal hemorrhage. Renal involvement impairs kidney function. Hepatic infiltration causes liver failure in advanced cases. Bone marrow replacement eliminates normal blood cell production. Metabolic derangements including hypercalcemia cause additional systemic effects. Death ultimately results from organ failure, metabolic collapse, or secondary complications of immune suppression.