medwireNews: Chemotherapy may only offer additional overall survival (OS) benefit over endocrine therapy alone for women with hormone receptor (HR)-positive, HER2-positive breast cancer size of 8–10 mm and not those with smaller tumors, report US researchers in a letter to JAMA Network Open.
Anurag Singh, from Roswell Park Comprehensive Cancer Center in Buffalo, New York, and co-workers collated information for 10,065 women recorded in the US National Cancer Database with pT1a–bN0 breast cancer during 2010–2015 who were followed up for a median of 41.8 months.
This included 5364 women who received hormone therapy and chemotherapy including HER2-directed treatment, and 4719 who received only hormone therapy, the team explains.
Multivariable analysis indicated that multiagent treatment was associated with significantly better OS than hormone therapy alone with a hazard ratio for death of 0.69, but that tumor size acted as a continuous variable, so that each 1 mm increase in size was associated with a significant hazard ratio of 1.07.
However, multivariable analysis performed for tumor size increments between 2 mm and 9 mm pointed to a cutoff of 8 mm for deriving OS benefit from chemotherapy, with a hazard ratio for death of 0.53 for patients with tumors sized 8–10 mm.
To test this finding, the team matched pairs of patients who did and did not receive chemotherapy by age, race, tumor characteristics, treatment history, and other sociodemographic factors.
Among the 1641 patients with a tumor size of less than 8 mm, there was no significant OS benefit with receipt of chemotherapy. By contrast, for the 648 patients with tumors of 8–10 mm, receipt of chemotherapy was associated with a significant hazard ratio for death of 0.48.
“It is evident that tumors 10 mm and smaller represent a heterogeneous group whose treatment should be tailored to improve the risk-to-benefit ratio of systemic therapy,” write Singh et al.
The authors acknowledge that their study is limited by the lack of data on the specific systemic therapies received by the patients, and await data from prospective studies such as the ATEMPT trial.
In the meantime, they suggest that their findings “can help clinicians in decision-making on adjuvant systemic therapy for patients with small HR-positive, ERBB2 [HER2]-positive breast cancers.”
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