Frequency and Role of CDKN2A Deletion in High-Risk Pituitary Neuroendocrine Tumors

The underlying mechanisms of aggressive pituitary neuroendocrine tumors (pitNETs) are still unclear. The p16 protein, encoded by the CDKN2A tumor suppressor gene on chromosome 9p21, is commonly reported to be lost in numerous types of cancer. For this reason, this study examined to examine the status of homozygous deletion of CDKN2A in high-risk pitNETs. Thirty-eight high-risk pitNETs (30 male, 8 female) were analyzed for CDKN2A deletion by fluorescent in situ hybridization (FISH). Demographic characteristics such as sex, patient age at operation, and sellar magnetic resonance imaging findings including tumor size and invasion status were recorded. The frequency of CDKN2A homozygous deletion by FISH was 3/38 (7.89%) in the high-risk pitNET group. All of these three cases with CDKN2A homozygous deletion were invasive densely granulated lactotroph tumors (p = 0.000). CDKN2A deletion was not correlated with patient age, sex, cavernous sinus invasion (CSI), and tumor size (p > 0.05). The Ki-67 proliferation index was significantly correlated with CDKN2A homozygous deletion (p = 0.003). The mean Ki-67 proliferation index was 10.7% in pitNETs with CDKN2A homozygous deletion and the Ki-67 proliferation index in the whole study group was 4.1%. CSI was significantly correlated with the morphofunctional tumor types including lactotroph tumor, invasive null cell tumor, and invasive gonadotroph tumor (p = 0.021). These findings suggest a close correlation between inactivation of p16 gene and invasive lactotroph tumors. Further investigations are needed to expand on the mechanism of p16 (CDKN2A) gene deletion in high-risk pitNETs.