A new Australian study has reported that women with stage IV breast cancer have better survival times if their tumors are progesterone receptor positive (PR+) than if they are progesterone receptor negative (PR-). The study was designed to compare the survival times of women with metastatic breast cancer according to whether their tumors had mixed estrogen receptor (ER) and PR status or hormone receptor positive (ER+/PR+) status. Data from three randomized phase III trials of aromatase inhibitors was used in the study. Both receptors were determined in 1,010 of the 1,870 women in the trials, including 31 that were ER-/PR-, which were excluded from the study. Of the remaining 979, 726 (74%) were ER+/PR+, 213 (22%) were ER+/PR- and 40 (4%) were ER-/PR+.

Although no differences were found in the apparent clinical benefit of treatment or time to progression, the median overall survival time of women with ER+/PR+ tumors (800 days) was found to be significantly longer than those with single receptor positive (ER+/PR- or ER-/PR+) tumors (600 days). Among only the women with ER+ tumors, the median overall survival of those with ER+/PR+ tumors (800 days) was significantly longer than those that were ER+/PR- (625 days). The authors conclude that PR status is an important prognostic factor for survival in metastatic breast cancer.

Study quantifies differences in survival times

This study quantifies median survival times for Australian women with stage IV breast cancer, based on ER+/PR+ compared to ER+/PR- tumor status. However, in some ways, it raises more questions than it answers for U.S. patients. It is remarkable than only 3% of the women for whom hormone receptor status was available were hormone receptor negative (ER-/PR-); the U.S. fraction is closer to 20% and Asian populations tend to have even higher proportions. It is well known that ER-/PR- tumors confer the worst prognosis, at least in the initial five years after diagnosis. However, hormone receptor negative tumors were excluded from the above study. Still, the worst survival in the study was found among women with ER-/PR+ tumors, suggesting that while PR status influences prognosis, ER status is yet more important.