PGR and medullary thyroid gland carcinoma: However, there was no significant difference in clinical stage, tumor size, lymphatic metastasis, rate of medullary carcinoma development, or estrogen receptor (ER) or progesterone receptor (PR) positivity.17,51 Kwong et al52 reported that BRCA mutation carriers were more likely than non-carriers to have cancers of higher histologic grade and triple negative cancers (48.3% vs 25.6%, P = 0.01).