Tumors originating in the pineal region, the endocrine gland responsible for the synthesis and secretion of melatonin (the hormone that regulates the sleep cycle), are exceedingly rare, accounting for less than 1 percent of primary central nervous system tumors. The most common of these tumors, comprising up to about 70 percent of pineal region tumors, are germ cell tumors. The pineal parenchymal tumor (PPT) is the second most common pineal tumor, making up between 10 and 30 percent of these already rare tumors. However, patients with PPT have a more difficult prognosis than those with other pineal tumors.
PPTs come from cells in the pineal gland called pinealocytes. These tumors are categorized as: well-differentiated pineocytoma (PC), PPT with intermediate differentiation (PPTID) and poorly differentiated pineoblastoma (PB). Patients with PC have the best prognosis, as this type of PPT is slower growing and offers better survival rates. PB cases, on the other hand, are very rare, very aggressive and commonly spread through the cerebrospinal fluid tract. PPTID cases, meanwhile, are quite unpredictable.
Because these tumors are so rare, there is some debate among researchers about the best way to treat them.