Increased erythropoietin levels are attributable to which of the following tumors?

Increased erythropoietin levels are associated with renal adenocarcinoma because this type of tumor can produce erythropoietin either directly or through a paraneoplastic syndrome. Renal tumors, particularly those that are vascular, can lead to increased production of erythropoietin which stimulates red blood cell production in the bone marrow, resulting in secondary erythrocytosis.

While other tumors may have various associated syndromes and complications, they typically do not lead to elevated erythropoietin levels like renal adenocarcinoma does. For instance, pancreatic adenocarcinoma primarily leads to metabolic derangements and does not notably produce erythropoietin. Small cell lung carcinoma is known for secreting antidiuretic hormone (ADH) and various neuroendocrine markers, not erythropoietin. Hepatocellular carcinoma might influence erythropoietin levels indirectly due to liver dysfunction, but it is not a primary source. Thus, renal adenocarcinoma stands out as the primary tumor directly responsible for elevated erythropoietin levels.