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High levels of tumour infiltrating lymphocytes (TILs) at diagnosis were shown to be associated with decreased distant recurrence rates in triple negative breast cancer (BC) and increased trastuzumab (T) benefit in HER2+ disease.1
However, conflicting data showed that HER2+ cases with high TILs might not benefit from the addition of T to chemotherapy.2 Moreover, emerging literature suggests association between high tumour-associated macrophages (TAMs) and poor prognosis in patients with BC.3
We conducted a retrospective study using the Sunnybrook Biomatrix database to quantify TILs and macrophages markers in an HER2+ BC population treated with neoadjuvant chemotherapy and explore their role in predicting the benefit from T.
Two independent pathologists with BC expertise reviewed all core biopsies to select the optimal slide for TILs assessment. Pathological complete response (pCR) was defined as no invasive residual in breast or nodes.
After using the self-training tutorial supplementing the published guideline recommendations,4 the two pathologists semiquantified stromal TILs using 4–5 µm thick H&E-stained slides. TILs were assessed as the percentage of tumour stroma containing infiltrating lymphocytes as a continuous scale. Cases with 60% TILs or more were categorised as lymphocyte-predominant BC (LPBC). CD68 Immunohistochemistry (IHC) was performed (prediluted KP-1; clone 790-2931; Ventana) on automated Benchmark Ultra platform in two runs using standard procedure. The proportion of CD68-positive stromal mononuclear cells of all TILs was evaluated using a double headed microscope and high CD68 ratio was defined as >60%. The inter-rater reliability was excellent (Cohen's κ 0.89).
Fifty-two patients were successfully assessed. Baseline characteristics are presented in table 1. In the neoadjuvant setting, 40 patients received chemotherapy and T (77%) and 12 patients had only chemotherapy (23%).
The pCR rate was 41% in the whole cohort (21/51) and …