The probability of lymph node metastasis in small invasive lung adenocarcinoma could be calculated by the following formula: ln (p/1-p) = -0.068 × age + 0.025 × SA + 0.098 × CA125 + 0.547 × mucinous (no = 0; yes = 1) + 2.927 × CK5/6 (no = 0; yes = 1)—13.972. The gene discussed is KRT5; the disease is metastatic malignant neoplasm in the lymph nodes.