Immune checkpoint inhibitors for patients with metastatic triple-negative inflammatory breast cancer (INCORPORATE): An international cohort study.

Background: Inflammatory breast cancer (IBC) is the most aggressive clinical presentation of breast cancer, recapitulating a specific biology with more immune-vulnerability than non-IBC. Patients with metastatic, triple-negative IBC (mTN-IBC) receive immune checkpoint inhibitors (ICIs) and chemotherapy, similarly to patients with triple-negative non-IBC. However, the benefit derived from ICI incorporation in this rare type of breast cancer is unknown.

Methods: We conducted a multicenter, international, retrospective, cohort study to evaluate the activity of ICIs in patients with metastatic, triple-negative, primary IBC, who received ICIs plus first line chemotherapy from January 2015 to April 2023. A sample size of 42 patients allowed to detect an increase in 6-months real-world progression-free survival (rwPFS) rate from 40 % with only chemotherapy to 60 % with ICI and chemotherapy.

Results: 41 patients from eight international IBC referral centers were included (61 % with primary, de novo mTN-IBC, 61 % with visceral disease). All received ICIs plus first line chemotherapy and 24 % underwent breast surgery and/or locoregional radiotherapy. After a median follow-up of 19.3 months, the 6-months rwPFS rate was 30 % (95 % Confidence Interval [CI], 17-45 %), the median rwPFS was 3.3 months (95 % CI: 2.2-5.4), the median overall survival was 15.7 months (95 % CI: 6.8-16.3).

Conclusions: This one-sample analysis showed a poor outcome of patients with mTN-IBC, despite the treatment with ICI, in contrast with the expected benefit based on preclinical evidence of immune-vulnerability of IBC. These results suggest the need to further investigate the role of immunotherapy in this aggressive and rare type of breast cancer presentation.