Endocrine therapy de-escalation a possibility for ER-low positive breast cancer

medwireNews: Women with estrogen receptor (ER)-low positive breast cancer may be considered for 2 to 3 years of endocrine therapy rather than the standard 5 years without a negative impact on disease-free survival (DFS), Chinese researchers report.

Writing in Cancer, Ke-Da Yu and colleagues, from Fudan University Shanghai Cancer Center, explain that the “optimal duration of endocrine therapy for ER-low positive breast cancer has not been established” and note that “it is unclear whether long-term treatment is still necessary for this subgroup.”

To address this, they identified 634 individuals from a prospectively maintained Breast Surgery Database who had early-stage breast cancer with a pathologically confirmed ER-low positive status, defined as 1% to 10% staining by immunohistochemistry.

Between 2012 and 2017, 89 (14.0%) patients received no endocrine therapy, 185 (29.2%) received 2 to 3 years of endocrine therapy, and 360 (56.8%) received approximately 5 years of endocrine therapy.

After a median 65 months of follow-up, the DFS rate was 78.3% in the women given no endocrine therapy, 84.2% among those given 2 to 3 years of endocrine therapy, and 87.7% among those given 5 years of treatment.

After adjustment for potential confounders, the researchers observed that the group given 5 years of endocrine therapy had a significant 46% lower risk for recurrence or death than the no endocrine treatment group, but there was no significant difference relative to the group given the shorter course of endocrine therapy.

There was also no significant difference in DFS between the two treatment durations in a propensity score-matched analysis in which 180 participants who received 5 years of endocrine therapy were matched to 180 who received 2 to 3 years of therapy on the basis of age, menopausal status, pathologic tumor size, lymph node status, tumor grade, HER2 status, and receipt of chemotherapy or radiotherapy.

Yu et al say that their findings are “of great significance for optimizing the treatment strategy of patients with ER-low positive breast cancer” and suggest that “de-escalation of 5 years’ duration might be considered for the ER-low positive population and not only may reduce the toxicities of long-term treatment but also may reduce the economic costs and improve patients’ compliance.”

However, they add: “Further studies of more extensive scale and translational research on identifying endocrine-sensitive cases within this population are still needed.”

In an accompanying editorial, Johanna Poterala and Kari Wisinski, both from the University of Wisconsin Carbone Cancer Center in Madison, USA, describe the study as “well designed” with “an impressive number of patients given the rarity of the ER-low subtype.”

Yet they also highlight a number of limitations, including the lack of randomization, exclusion of patients who received neoadjuvant chemotherapy, and lack of progesterone receptor quantification, that mean further validation is needed before the findings become practice-changing.

Poterala and Wisinski say that although “a shortened duration of endocrine therapy can be considered given these results, the decision between 5 years versus 2 to 3 years should be a discussion between the patient and their oncologist and will likely depend on each patient’s preference.”

They add: “If the patient is having issues with medication tolerance, a shortened duration of 2 to 3 years is supported by this study.”

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Cancer 2022; doi:10.1002/cncr.34155
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