Tumor-infiltrating lymphocytes status, programmed death-ligand 1 expression, and clinicopathological features of 41 cases of pure apocrine carcinoma of the breast: a retrospective study based on clinical pathological analysis and different immune statuses.

Background: Pure apocrine carcinoma (AC) of the breast can be divided into human epidermal growth factor receptor-2 (HER2)-positive and triple-negative apocrine carcinoma (TNAC). Some studies showed that triple negative breast cancer with low tumor-infiltrating lymphocytes (TILs) and high programmed death-ligand 1 (PD-L1) status may be a therapeutic target for immune checkpoint inhibitors. However, the clinicopathological features of different HER2 expression, TILs status and PD-L1 expression in AC are not clear. Therefore, we investigate the status of TILs and PD-L1, as well as the clinicopathological features of pure apocrine carcinoma of the breast. Methods: We retrospectively analyzed the clinicopathological data, and prognosis of 41 cases of pure apocrine carcinoma of the breast that underwent surgical resection from January 2014 to November 2020. TILs were evaluated. Immunohistochemistry (IHC) staining was applied to detect PD-L1 protein expression in 14 of these samples from January 2019 to November 2020. The expression and correlation of HER2, TILs, PD-L1 and clinicopathological features and prognoses were analyzed. Results: A total of 80.5% (33/41) of patients had TILs <50%, and 19.5% (8/41) had TILs ≥50%. The expression of TILs and the Ki-67 proliferation index were significantly higher in the HER2-positive group (41.5%, 17/41) compared to the HER2-negative group (58.5%, 24/41) (P<0.05). Approximately 52.9% (9/17) of HER2-positive patients treated with Trastuzumab targeted therapy, overall survival was higher in HER2-positive patients than in HER2-negative patients (P=0.211). The PD-L1 positivity rate was 50% (7/14) in the 14 pure apocrine carcinoma of the breast samples, and 66.7% (4/6) and 37.5% (3/8) in the HER2-negative and HER2-positive groups, respectively, with no significant difference (P=0.592). Among these 14 cases, two samples had TILs ≥50%, both of which were positive for PD-L1 and Ki67 >20%; and 12 cases had TILs <50%, of which 41.7% (5/12) were PD-L1-positive and 58.3% (7/12) were PD-L1-negative. All 14 cases with PD-L1-negative had TILs <50%. There was no significant difference in overall survival between TILs and Ki67 co-expression (P=0.452). Conclusions: Pure AC HER2-positive patients have higher levels of TILs and Ki67, HER2 negative and TILs ≥50% patients may have higher PD-L1 expression, which may be helpful for screening patients with different immune statuses to guide effective clinical treatment combinations.