Solid histological component of adenocarcinoma might play an important role in PD‐L1 expression of lung adenocarcinoma

BACKGROUND: In this study we aimed to clarify the PD‐L1 positive expression in lung adenocarcinoma, including various adenocarcinoma subtypes paying particular attention to its component. METHODS: A total of 307 lung adenocarcinoma patients who underwent lobectomy or segmentectomy, as well as systematic lymph node dissection (ND2a), from February 2008 to March 2020 at our hospital, were enrolled into the study. A final diagnosis of adenocarcinoma was obtained from the resected lung specimens of all 307 patients to determine the histological type, adenocarcinoma subtype, and component of adenocarcinoma by ethics of 5%. PD‐L1 was immunohistochemically stained using the murine monoclonal antibody clone 22C3. RESULTS: When PD‐L1 expression‐positive was defined by tumor proportion score (TPS) ≥1%, the positive cases were 6/33 in adenocarcinoma (Ad) in situ (AIS), 2/26 in minimally invasive Ad (MIA), 12/60 in lepidic predominant Ad (LPA), 44/91 in papillary predominant Ad (PPA), 24/49 in acinar predominant Ad (APA), 23/28 in solid predominant Ad (SPA), 4/7 in micropapillary predominant Ad (MPA), and 0/13 in invasive mucinous Ad (IMA). In the high proportion group (APA, PPA, SPA, and MPA) of PD‐L1 expression, SPA was the only subtype which was statistically significant when both PD‐L1 expression‐positive was defined by TPS ≥ 1% (p < 0.0001) and TPS ≧ 50% (p < 0.0001). We then considered the solid component. We investigated 279 cases of the other subtype group excluding SPA. The group containing a solid component (≥5%) tended to be PD‐L1 expression‐positive both when defined by TPS ≥1% (p < 0.0001) and TPS ≧50% (p = 0.0049). CONCLUSIONS: The PD‐L1 expression tended to be positive when a solid component was confirmed (≥5%) in specimens of lung adenocarcinoma patients.