The following article features coverage from the 2020 San Antonio Breast Cancer Symposium. Click here to read more of Cancer Therapy Advisor‘s conference coverage.

Combining neoadjuvant pembrolizumab with radiotherapy prior to standard of care chemotherapy may increase pathologic complete responses rates in women with triple-negative breast cancer (TNBC), according to results presented in a poster at the 2020 Virtual San Antonio Breast Cancer Symposium (SABCS) by Heather L. McArthur, MD, PhD, of Cedar-Sinai Medical Center, Los Angeles, California, and colleagues.

The trial looked at preoperative pembrolizumab plus radiotherapy in 20 patients with TNBC for whom lumpectomy and adjuvant radiotherapy was planned. Neoadjuvant pembrolizumab was given at 200 mg followed 3 weeks later with pembrolizumab at 200 mg plus radiotherapy (8 Gy/3 fractions) to the primary breast tumor, followed by standard-of-care neoadjuvant chemotherapy.

Sixty percent of patients achieved a complete response and 15% of patients had a near-complete response. Three patients did not complete the planned course of chemotherapy; 2 patients did not complete the course because of residual disease, and 1 patient achieved a complete response after weekly chemotherapy.

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Of the 10 patients with node-positive disease at diagnosis, 70% became ypN0, 1 patient became ypN1mic, and 2 became ypN1a at the time of surgery.

The researchers observed no grade 3 or 4 toxicities during the combination treatment. Grade 4 colitis was reported in 1 patient during chemotherapy and was attributed to pembrolizumab.

The researchers noted that changes in TILs after pembrolizumab plus radiotherapy did not correlate with treatment response. All responders had a baseline TIL count of 10% or greater; this was associated with pathologic complete response. None of the patients with TIL count lower than 10% achieved a pathologic complete response.

A phase 2 expansion trial is currently accruing.

Disclosure: This study was supported by the Breast Cancer Research Foundation.

Read more of Cancer Therapy Advisor‘s coverage of the 2020 SABCS meeting by visiting the conference page.


McArthur H, et al. Pre-operative pembrolizumab (pembro) with radiation therapy (RT) in patients with operable triple-negative breast cancer (TNBC). Presented at: 2020 Virtual San Antonio Breast Cancer Symposium (SABCS); December 8-11, 2020. Abstract PS12-09.