This is the first case of Cushing's syndrome secondary to ectopic ACTH secretion where the presence of ACTH by immunohistochemistry and the expression of the POMC gene by RT-PCR have both been demonstrated in a breast carcinoma with metastases.
Overall, pituitary carcinoma metastases showed an average of 8.3 chromosomal imbalances per tumor (7 gains vs 1.3 losses), 10 in prolactin cell carcinoma metastases (7.5 gains vs 2.5 losses) and 6.5 in ACTH cell carcinoma metastases (6.5 gains vs 0 loss).
The length of POMC mRNA in MTCs (present in all 4 metastases investigated but not in 7 primary tumors) and pheochromocytomas is about 100 nucleotides more than pituitary POMC RNA.
Compared with the POMC mRNA occurring in the human pituitary gland, the size of the RNA species hybridizing to the POMC-specific probe was larger in the metastases of both of the patients investigated. cDNA complementary to mRNA from one of the metastases was cloned into pBR 322.