Breast cancer that is progesterone receptor positive (PR+), estrogen receptor negative (ER-) and not HER2 overexpressing (HER2-) is relatively rare, accounting for up to 6% of cases. Therefore, this type is not well studied. Generally speaking, patients with tumors that are positive for either ER or PR are considered hormone receptor positive for purposes of making treatment decisions. In fact, ER-/PR+ disease has been found to be somewhat responsive to endocrine therapy (tamoxifen or an aromatase inhibitor), although less so than ER+/PR+ disease. ER-/PR+ breast cancer has been found to be somewhat more aggressive than ER+/ER+ disease. For example, locoregional recurrence rates are higher in women with mixed hormone receptors compared to those with ER+/PR+ disease (8.8% compared to 2.5% during the first seven years after diagnosis in one study). Now a new Chinese study has reported that ER-/PR+/HER2- breast cancer has outcomes similar to that of triple negative (ER-/PR-/HER2-) disease.

Latest research finds ER-/PR+/HER2- and TN disease have similar outcomes

The study referenced above was designed to investigate the role of PR+ status in ER-/PR+/HER2- breast cancer by comparing this subtype to triple negative (ER-/PR-/HER2-) disease. To conduct the study, the authors examined 3,966 invasive breast cancer cases operated on between 2005 and May 2008 at Cancer Hospital, Chinese Academy of Medical Sciences. A total of 240 (6%) of the cases were classified as ER-/PR+/HER2- and 348 (9%) were triple negative.

Compared to triple negative disease, ER-/PR+/HER2- tumors tended to have lower grade (Grade 3: 45.7% vs. 37.5%) and smaller tumor size. However, no statistically significant differences in relapse-free survival or overall survival were found between the two types. The five-year overall survival rate was approximately 87% for both. However, women with ER-/PR+/HER2- disease who received endocrine treatment had better relapse-free and overall survival than those who did not. The authors conclude that ER-/PR+/HER2- breast cancer has aggressiveness similar to that of triple negative disease, suggesting that it should be regarded as biologically distinctive group. In addition, PR+ status is not necessarily a good prognostic factor when combined with ER-. However, the authors note, endocrine therapy still appears to benefit this group of patients. Further studies are warranted to uncover the underlying mechanisms for the behavior of ER-/PR+/HER2- disease.

Please see our article on ER-/PR+ breast cancer for more information.