What causes a prolactinoma to be aggressive or to become a pituitary carcinoma?

Malignant prolactinoma is an exceedingly rare endocrine tumor and cannot be diagnosed on histological grounds alone. Similarly to other neuroendocrine tumors such as pheochromocytoma, the mitoses index, Ki-67, p53, and others are utilized in helping understand whether a tumor is benign or malignant or to better predict tumor behavior. We here present the unusual case of an unfortunate young man with an aggressive prolactinoma, the complications of which led to his premature death.

A 25-year-old white man developed severe headaches, low energy, and decreased libido. A brain magnetic resonance imaging (MRI) showed a 4 x 3 x 2 cm pituitary tumor invading the left cavernous sinus. Laboratory findings revealed elevated prolactin (470 ng/mL) and adrenocorticotropic hormone (ACTH, 82 pg/ml) and decreased total testosterone (176 ng/dl). Visual fields showed superior quadrantanopia in the left eye. Transsphenoidal pituitary resection was undertaken. Pathology revealed a prolactinoma with atypical cells, diffuse p53 nuclear labeling, and a Ki-67 index of 23% (high). Postoperatively, prolactin remained elevated (725-891 ng/ml) and cabergoline was increased to 1 mg three times weekly, with serum prolactin further increasing to 3507 ng/ml five months postoperatively. Repeat MRI revealed extension of the tumor with optic chiasm compression and left orbit invasion. Because of acute left vision loss with ophthalmoplegia, an urgent left frontotemporal craniotomy and tumor resection were conducted. The Ki-67 index of the tumor was 24.8%, the mitotic figure immunostain phosphohistone-H3 positive. Sixty percent (60%) of tumor cells were positive for p53. Cabergoline was increased to 1 mg daily but prolactin remained elevated (770 ng/ml). The patient then underwent proton beam radiation to the area of concern involving the sella. Prolactin thereafter improved to 44 ng/ml. He then developed acute vision loss of the right eye with an MRI showing tumor in the right cavernous sinus. A 15 mm dural-based right temporal mass believed to be a metastasis was also noted. Following this scan, he was considered too high risk for debulking surgery and instead underwent gamma knife irradiation to the sella area. This shrank the right cavernous sinus tumor mass, while the right temporal mass increased in size. The patient developed blindness and left-sided weakness and required enteral feeding and tracheostomy after prolonged intubation. A trial of chemotherapy with temozolomide (350 mg daily for 5 days) near the end of his life was unsuccessful. He died on home hospice 31 months after his first surgery.

Headaches, vision changes, and symptoms of androgen deficiency syndrome can be manifestations of an aggressive prolactinoma that might require surgery and additional medical therapy including cabergoline and temozolomide with an unpredictable time of survival.