- In this problem-oriented review of abnormalities associated with cancer, we have emphasized distinctive diagnostic points related to pathogenesis for each condition and outlined how the approach to management is determined by pathogenesis. For abnormalities of the complete blood count, it is important to distinguish between abnormalities directly related to marrow malignancy and abnormalities associated with extramarrow malignancy. Hemopoietic tumors consist of developmentally deficient blood cells produced by a clonal population of malignant stem cells. Tumors infiltrating marrow cause overcrowding in the limited marrow microenviroment. Extramarrow malignancies cause blood abnormalities, but the potential for normal marrow function is present. Abnormalities of blood cells secondary to therapy are usually clearly identified by consideration of clinical history. The initial differential diagnosis for hypercalcemia is malignancy. An aggressive diagnostic approach may be needed to identify the neoplasm, and therapy should incorporate measures to prevent renal failure. Hypoproteinemia and hyperproteinemia may be caused by neoplasia. Monoclonal gammopathies should be identified and may be associated with hyperviscosity syndrome. Hypoglycemia in the adult animal is most frequently caused by insulin-secreting tumors, but it has also been associated with hepatic and other tumors. Increased blood urea nitrogen, creatinine, lipase, amylase, and liver enzyme activities may also be caused by malignancy. Inadequate urine concentrating ability may be caused by hypercalcemia or malignancy-associated renal insufficiency. Hematuria in older animals is suggestive of urinary tract neoplasia. Exfoliated tumor cells may be identified in the urine sediment of these patients.