FIGURE 1.

Representative micrograph showing the histopathological features of two primary breast mucoepidermoid carcinomas. Case #05 was a low‐grade carcinoma showing cystic ductal spaces lined by mucinous epithelial cells showing an unremarkable degree of nuclear pleomorphism and no mitotic count (A, H&E original magnification ×100; inset original magnification ×400), surrounded by a paucicellular myxoid stroma, as highlighted by Alcian blue stain (B, original magnification ×200). No PD‐L1 positivity was restricted to the neoplastic cells, with a CPS score of 10 (C, original magnification ×200). This neoplasm showed moderate cytoplasmic staining for EGFR in the majority of tumor cells and was scored as 2+ (D, original magnification ×200), while AREG expression was low (E, original magnification ×200). Case #3 was a high‐grade carcinoma showing nests of tumor cells with mucinous and squamoid features with no keratinization, minimal/null cystic formation, variable degree of nuclear atypia, occasional mitoses, karyopyknosis (F, H&E original magnification ×100; inset original magnification ×400), and diminished stromal mucin production in the presence of sparse mucin pools between the neoplastic clusters (G, original magnification ×200). The presence of TILs was confirmed by the expression of PD‐L1, with a CPS scored as 25 (H, original magnification ×200). This neoplasm was EGFR‐positive (I, original magnification ×200) and AREG low (J, original magnification ×200).