Paraneoplastic Syndromes – Part 2 of 2
Central Toronto Veterinary Referral Clinic
Kevin Finora DVM, Diplomate ACVIM (Oncology and Small Animal Internal Medicine)
Paraneoplastic Syndromes – Part 2 of 2
Cancer has many effects on the body besides the local effect of the tumour. Paraneoplastic syndromes are effects of the cancer occurring distant to the tumour. Last month I discussed hypercalcemia as a paraneoplastic syndrome and this month I will review some of the other important paraneoplastic syndromes.
Hypoglycemia is a paraneoplastic syndrome commonly seen with various types of cancer. Paraneoplastic hypoglycemia is often thought to be restricted to patients with insulinoma only. With insulinomas, hypoglycemia develops secondary to excessive production of insulin by tumour beta-islet cells.
However, there are several other cancers that can lead to the development of decreased blood glucose. Hepatocellular carcinoma will commonly cause hypoglycemia. Leiomyosarcoma is an intestinal tumour which also often results in hypoglycemia. In patients discovered to have an intestinal mass and hypoglycemia, leiomyosarcoma must be considered a top differential. The pathogenesis of hypoglycemia associated with tumours other than insulinomas is variable. Hypoglycemia can be induced by increased tumour utilization of glucose (resulting in cancer cachexia). Neoplasia can also lead to changes in hepatic metabolism which decrease glycogenolysis and gluconeogenesis. Inhibition of glycogenolysis and gluconeogenesis will cause circulating blood glucose levels to fall. Many tumours have been demonstrated to produce the insulin-like growth factor (IGF). This growth factor acts in a similar manner to insulin and will lower blood sugar. If an animal has low blood glucose due to increased IGF production, a paired glucose insulin level will demonstrate both low glucose and insulin values. Insulin like growth factors levels can be assessed at most reference labs.
Anemia is another common paraneoplastic syndrome. There are many pathogeneses of cancer-associated anemia. These causes can be broken down to bone marrow and metabolic causes. In bone marrow based anemia the problem is related to a non-functioning marrow. Changes in marrow function are most often the result of infiltration of cancer into the bone marrow (myelophthisis). This “crowding out” of normal bone marrow represents a loss of normal functional marrow mass, resulting in decreased production of red blood cells. Another common cause of paraneoplastic anemia is secondary to chronic disease. Anemia of chronic disease is a disorder of iron metabolism. In these cases, serum iron levels are generally normal but the ability of the body to utilize iron for the metabolism of red blood cells (RBC) is altered. The end result is a depressed ability to form RBC. Cancer may also induce abnormal activity within the immune system. Immune mediated hemolytic anemia can be seen in cancer patients. Therefore neoplasia is always a differential to be assessed when a pet is diagnosed with immune mediated disease.
Understanding and recognizing paraneoplastic syndromes is an essential part of cancer diagnosis and treatment. These syndromes are often sentinels of disease and, more importantly, can be of immediate and life threatening concern to the patient. It is not unusual for there to be a need to concurrently treat a paraneoplastic syndrome while moving forward with a complete patient work-up.
Treatment of paraneoplastic syndromes must be targeted towards the underlying cause. Achieving this goal typically means addressing the cancer with surgery, radiation or chemotherapy. It must be kept in mind that when the primary cause of the paraneoplastic syndrome is addressed, there will be a lag time until resolution of the abnormalities is noted. Therefore treatments such as glucose administration, insulin receptor antagonism, and blood transfusions may be necessary in the short term.
Dr. Kevin Finora is a Board Certified Oncologist and Small Animal Internist who is part of the Healthcare Team at the Central Toronto Veterinary Referral Clinic. He is available for referrals and consultations Monday to Thursday (including Monday and Tuesday evenings). Please contact him with any oncology questions or concerns.