Pathological high malignant grade is higher risk of recurrence in pN0M0 invasive lung adenocarcinoma, even with small invasive size

INTRODUCTION: Tumor size is an absolute recurrence risk in lung cancer. Although morphological features also reflect recurrence risk, its significance among lower‐risk cases characterized by small size is unknown. We aimed to evaluate the relationship between pathological invasive tumor size and morphological features, and their prognostic impact by considering them simultaneously in lung adenocarcinoma. PATIENTS AND METHODS: We retrospectively reviewed 563 pN0M0 patients with pathological invasive size of ≤40 mm. The patients were classified by pathological invasive size and pathological malignant grading using the proportion of subhistological components. The prognostic impact was evaluated using recurrence‐free survival (RFS) and overall survival (OS). The impact on prognosis was evaluated using uni‐ and multivariate analyses. RESULTS: The proportion of histological grade changed according to invasive tumor size. Patients with high malignant grade (G3) showed worse RFS than those with low and intermediate malignant grade (G1+2) with invasive size ≤20 mm. The 5‐year RFS (G1+2 vs. G3) in 5–10 mm was 96.0% vs. 83.3% (HR = 5.505, 95% CI = 7.156–1850, p < 0.001) and in 10–20 mm was 87.8% vs. 67.1% (HR = 2.829, 95% CI = 4.160–43.14, p < 0.001). G3 patients were significantly bigger in invasive size and included more pleural/lymphatic/vascular invasion and recurrence. Multivariate analysis indicated pathological G3 status was significantly associated with worse RFS (HR = 2.097, 95% CI = 1.320–3.333, p = 0.002). CONCLUSIONS: Invasive tumor size and pathological malignant grade overlap in invasive adenocarcinoma. G3 patients are more likely to have pleural/lymphatic/vascular invasion and significantly worse RFS compared to G1/G2 cases, even with a small invasive size of ≤20 mm.