Breast cancer (BC) is the most common
cancer among women. It is known that the
prolactin receptor (PRLR) may play a role in breast
carcinogenesis, but the available data are often contradictory. To get a more complete picture of the relationship between the receptor and mammary gland
carcinogenesis, we examined the association between changes in PRLR expression level and
tumor subtype (and its main characteristics). To do this, using real-time PCR, we evaluated the level of PRLR
mRNA in BC tissue samples and untransformed adjoining tissue samples (89 pairs). Since the
androgen receptor (AR) has begun to be seen as a prognostic marker in
breast cancer, we also evaluated the association between
mRNA levels of AR and PRLR. We found a significant increase in PRLR expression in
luminal subtypes; the highest level of PRLR
mRNA was detected in
luminal A subtype. In HER2-positive ER-, PR-negative BC, the PRLR
mRNA level decreases in
tumor tissues compared with untransformed tissues. High PRLR expression is also associated with smaller
tumor size in
luminal B HER2-negative subtype. In ER-, PR-negative
tumors, PRLR expression is associated with AR expression: PRLR
mRNA level is increased when AR
mRNA level is reduced by more than 8 times in triple-negative
tumors; in contrast, in HER2-positive subtype it decreases more significantly when AR expression is reduced by more than 3 times. A tendency towards an increase in PRLR expression with an increase in the AR
mRNA level was also discovered in
luminal subtypes. The level of PRLR expression depends on the age of patients. In
luminal A, PRLR expression is higher in patients under 65 years. In contrast, in
luminal B HER2-negative and triple-negative BC, reduced PRLR expression was observed in patients under the age of 40 years and under the age of 50 years, respectively. In this group of patients under the age of 40 years with
luminal B HER2-negative BC, ER expression was also reduced (0-4 score according to the IHC assay). Thus, PRLR probably plays a different role in the development and progression of BC: in
luminal A and
luminal B HER2-positive subtypes PRLR may act as an
oncogen, and in
luminal B HER2-negative and ER-, PR-negative subtypes can play a
tumor suppressor role.