Are aggressive pituitary tumors and carcinomas two sides of the same coin? Pathologists reply to clinician's questions

Pituitary adenohypophyseal tumors are considered as benign and termed adenomas. However, many tumors are invasive and a proportion of these exhibit an aggressive behavior with premature death due to progressive growth. Only very rare (0.2%) tumors with metastases are considered malignant and termed carcinomas. Taking into account this variability in behavior and the oncological definition, pathologists have proposed changing the term adenoma to tumor. Here we explain why use the term tumor instead of adenoma and identify tumor characteristics, associated with a high risk for poor prognosis. In a cohort of 125 tumors with aggressive behavior (APT) and 40 carcinomas with metastases (PC), clinical and pathological features were very similar. The comparison of this cohort (APT+PC) with a reference surgical cohort of 374 unselected patients clearly shows that the two cohorts differ greatly, especially the percentage of tumors with Ki67 >= 10% (35%vs3%; p < 0.001). A five-tiered prognostic classification, associating invasion and proliferation, identified grade 2b tumors (invasive and proliferative), with a high risk of recurrence/progression. Because half of the APT+ PC tumors have a Ki67 index >= 10%, and 80% of them show 2 or 3 positive markers of proliferation, we suggest that tumors that are clinically aggressive, invasive and highly proliferative with a Ki67 >= 10%, represent tumors with malignant potential. The percentage of grade 2b tumors, suspected of malignancy, which will become aggressive tumors or carcinomas is unknown. It is probably very low, but higher than 0.2% in surgical series. Early identification and active treatment of these aggressive tumors is needed to decrease morbidity and prolong survival.