MAX genomic inactivation is associated with p16 silencing in the absence of p16 coding sequence deletion and MAX induction restores p16 expression and inhibits GIST proliferation.
The expression of the nuclear and cytoplasmic forms of p16 represent two independent mechanisms, and both seemed to control proliferation in response to oncogenic stimuli, protecting the cell from malignant transformation in BRAF-mutated GISTs.
Furthermore, p16 positivity varied between the control sarcomas based on tumor type as follows: 11/11 leiomyosarcomas, 8/11 pleomorphic undifferentiated sarcomas, 9/39 sarcomatoid carcinomas, 7/7 desmoid tumors, 1/3 endometrial stromal sarcomas, and 1/2 malignant gastrointestinal stromal tumors.
Molecular studies and p16 status confirmed the typical characteristics of gastrointestinal stromal tumors with an aggressive phenotype underscoring the need for a special interdisciplinary treatment and for achieving complete local excision with free margins.
The coincidence of loss of p16 and overexpression of human telomerase reverse transcriptase seems to be in contradiction to the small size, the benign nature, and the limited growth potential of appendiceal gastrointestinal stromal tumors.
We have previously investigated the role of loss of p16(INK4A) by loss of heterozygosity and immunohistochemistry in the progression of GISTs and found that loss of heterozygosity of 9p and loss of p16 expression are confined to malignant GISTs.