Pathological response after pembrolizumab-based chemotherapy in triple-negative breast cancer is heterogeneous

Design

Retrospective histopathological study of baseline and post-treatment specimens

Population

203 patients with early triple-negative breast cancer given neoadjuvant chemotherapy with pembrolizumab, then surgery

Primary outcome

Pathological response in breast and nodes, and its relation to outcome

Effect

pCR 63.1%; complete nodal response 23.6%; single confined residual focus 51.4% of non-pCR cases

This histopathology study reviewed baseline biopsies and post-treatment specimens from 203 patients with early triple-negative breast cancer who had neoadjuvant chemotherapy with pembrolizumab, followed by surgery.

Pathological complete response was reached in 63.1%. Higher histological grade, more tumour-infiltrating lymphocytes and a higher Ki-67 index were independently associated with complete response. In patients without complete response, residual disease was most often a single confined focus (51.4%). Fibrotic tumour beds were more common without complete response, and stromal elastosis was more common with it. Nodal response was heterogeneous: complete in 23.6%, none in 8.4% and mixed in 7.4%.

Recurrence was more frequent without complete response, and with multifocal baseline tumours, higher clinical T stage, rare subtypes, low lymphocyte infiltration and residual nodal disease. For the pathologist, the message is to describe residual disease pattern, tumour bed change and nodal response in detail, not only to report a yes-or-no pCR.

• Report residual cancer burden, residual disease pattern and tumour-bed features in post-treatment breast specimens.
• Assess and report nodal response separately; mixed and non-response patterns occurred.
• Record baseline grade, TILs and Ki-67 on the pre-treatment biopsy report.
• Sample the tumour bed generously, since residual disease is often a single focus.
• Do not use these associations to predict an individual patient's outcome.

Why it matters

A single pCR label hides differences in the tumour bed and nodes that relate to recurrence.

Don't overread it

A retrospective single-study pathology review with no randomised comparison; it does not show that detailed reporting changes treatment.

The statistics, in plain English

'Independently associated' means the link remained after adjusting for the other factors in the model, which is not the same as causing the response. Subgroups defined by pattern are small, so differences in recurrence between them are suggestive only.

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