Which tumors are commonly associated with polycythemia as a paraneoplastic syndrome?

Polycythemia as a paraneoplastic syndrome often occurs due to the production of erythropoietin (EPO) by tumors, which stimulates red blood cell production in the bone marrow. Both renal cell carcinoma and pheochromocytoma are tumors known for producing excess EPO.

Renal cell carcinoma, in particular, is the most common solid tumor associated with secondary erythrocytosis. This cancer can produce ectopic EPO, leading to increased red blood cell mass. Similarly, pheochromocytoma, which is a tumor of the adrenal glands, can also secrete EPO, contributing to polycythemia.

On the other hand, hepatocellular carcinoma and hemangioblastoma are also known to be associated with paraneoplastic conditions, including polycythemia due to EPO production. Hepatocellular carcinoma can produce various cytokines and growth factors, including EPO. Hemangioblastomas, particularly those associated with von Hippel-Lindau disease, can lead to increased EPO levels due to their vascular nature and potential to secrete the hormone.

Given that both sets of tumors can lead to the paraneoplastic syndrome of polycythemia through different mechanisms of EPO secretion,