Historically, pituitary tumors have been classified as carcinomas if they spread to other tissues in a discontinuous fashion. This implies that a metastasis confirmed and documented by biopsy must be present in a patient with a pituitary tumor before a diagnosis of cancer can be made.
Most pituitary carcinomas have been diagnosed postmortem based on a history of an aggressive pituitary tumor. The autopsy often demonstrates metastases to the neuraxis, liver, or other tissues. In some of our patients, “drop metastasis” to cervical lymph nodes have been a presenting feature, defining the malignant nature of aggressive pituitary tumors. It is not uncommon to see patients with giant macroadenomas that invade parasellar structures or compress brain tissue without known metastases. In other organ systems, neoplasms that cross tissue planes in a similar manner would be characterized as malignant. Why not pituitary tumors?
Advances in molecular biology have led to a better understanding of the biology and growth patterns as well as clinical behavior of pituitary tumors. The Ki-67 labeling index, an immunochemical marker of tumor cells in a phase of the cell cycle other than the resting phase, correlates with tumor behavior. Tumors with a high Ki-67 labeling index are more likely to be invasive and aggressive lesions at risk for recurrence. Extensive p53 immunoreactivity classifies a tumor as atypical and portends a worse prognosis. Both of these markers are employed in the evaluation and management of our patients at the California Center for Pituitary Disorders at UCSF. These tests, along with other clinical and radiographic parameters, allow us to educate our patients about the likelihood of recurrent disease, progression of residual disease, and permit us to tailor our follow-up plan to their specific needs.
Written by Lewis Blevins, Jr., MD