Recent case reports have documented the efficacy of
temozolomide therapy in some aggressive
pituitary adenomas and
pituitary carcinomas resistant to multimodality
therapy. Evidence suggests that low O6-methylguanine-DNA
methyltransferase (MGMT) immunoexpression correlates with response to
temozolomide chemotherapy. Herein, we aimed to study MGMT immunoexpression in a spectrum of
pituitary tumors, indolent, aggressive and malignant. A literature review of the use of
temozolomide in
pituitary tumors was also performed. Immunohistochemistry for MGMT was performed on 60
pituitary tumors identified in the Mayo Clinic Tissue Registry and the consultation files of one of us (BWS). The group included 30
pituitary carcinomas (15
ACTH, 10 PRL, 1 FSH/
LH, 1 TSH, 1 silent subtype 3 and 2 null cell). Tissue from recurrences was available in 17 cases. In addition, 30 functionally different
pituitary adenomas were studied, including 15 invasive and 15 non-invasive
adenomas. Overall, 32 cases of
pituitary tumors (54%) demonstrated low MGMT immunoexpression. This included 17 of 30 (57%)
carcinomas, 9 of 15 (60%) invasive
adenomas, and 6 of 15 cases (40%) of non-invasive
pituitary adenomas. There was no significant change in MGMT immunoexpression between primary and recurrent
tumors.
Prolactin-producing
carcinomas had the highest proportion of
tumors (80%) with low expression. A significant proportion of
pituitary adenomas and
carcinomas demonstrate low MGMT immunoexpression. In an effort to anticipate the likelihood of a
temozolomide response, all cases of aggressive
pituitary tumors should be assessed for MGMT expression.