Transformation of a pituitary macroadenoma into to a corticotropin-secreting carcinoma over 16 years

To describe a case of a pituitary macroadenoma that differentiated into a corticotropin (ACTH)-secreting carcinoma with metastasis to the thigh. We present a case report with a 16-year follow-up that includes anatomic and endocrine documentation of the history of an ACTH-secreting carcinoma. A 32-year-old woman presented for evaluation in 1989 because of visual field defects. Magnetic resonance imaging revealed a locally invasive 3-cm macroadenoma. She had no clinical signs of cortisol excess. The patient underwent surgical debulking followed by a course of radiation directed to the pituitary. Results from retrospective immunohistochemical staining with antibodies against ACTH, prolactin, and MIB-1 were negative. Postoperatively, she could not be weaned from exogenous steroids without developing symptoms of adrenal insufficiency. In 1995, she developed left facial palsy and diplopia caused by tumor growth. In 1997, the patient developed progressive symptoms of cortisol excess, which continued after exogenous steroid replacement was discontinued. The patient's clinical status continued to deteriorate because of local mass effect from tumor growth and uncontrolled hypercortisolism. She underwent bilateral adrenalectomy in 2003. The patient remained debilitated in a long-term care facility for 2 years when she was found to have a mass on her left hip. Biopsy results of the obturator muscle revealed metastatic tumor of neuroendocrine origin with strong reactivity to ACTH antibodies and MIB-1 labeling in 8% of tumor cell nuclei. A pituitary tumor can transform into an ACTH-secreting carcinoma in an indolent manner. Patients with invasive pituitary adenomas require long-term surveillance to monitor for differentiation into pituitary carcinoma.