[Pituitary lactotroph adenomas resistant to dopamine agonist treatment: histological and immunohistochemical characteristics].

OBJECTIVE: To present the histological and immunohistochemical characteristics of pituitary lactotroph adenomas (PLAs) resistant to dopamine agonist treatment.

SUBJECT AND METHODS: The investigators examined paraffin-embedded blocks and histological sections obtained from 19 patients (13 women, 6 men), whose median age was 29 (19, 38) years, after surgical treatment (adenomectomy) for PLAs resistant to dopamine agonist treatment. Immunohistological examination was performed using antibodies against prolactin (PRL), growth hormone (GH), thyroid-stimulating hormone (TSH), adrenocorticotropic hormone (ACTH), luteinizing hormone (LH), follicle-stimulating hormone (FSH), type 2 dopamine receptors (DR2 ), estrogen receptors-α (ERα), the proliferation marker Ki-67, and the endothelial cell marker CD34.

RESULTS: The expression of PRL by adenoma cells was revealed in all the patients. The coexpression of PRL and GH without clinical and laboratory signs of acromegaly was established in 3 cases. No expression of TSH, ACTH, LH, or FSH was revealed in any cases. Positive immunoreaction using antibodies against DR2 and ERα was detected in 8 and 6 cases, respectively. No expression of any of the studied receptors was found in 6 patients. Ki-67 was more than 3% in 3 patients and higher in patients with supra- or retrosellar growth. There was a positive correlation between the serum level of Ki-67 and that of PRL at the onset of the disease. There were 37 (25, 85) adenoma vessels, as measured by CD34 immunoexpression. It was ascertained that the patients with parasellar adenoma had more tumor vessels than those without parasellar growth of adenoma and that with the latter invading the cavernous vessels, the number of vessels was statistically significantly more.

CONCLUSION: PLAs resistant to dopamine agonists in addition to PRL (100%) can express GH in 16% of cases are characterized by the immunoexpression of DR2 (42%) and ERα (32%), a low proliferative activity, increased angiogenesis in the adenomas with parasellar growth and invasion into the cavernous sinus.