The European Society for Medical Oncology (ESMO) guidelines in 2022 newly included decision tree algorithms for the differential diagnosis of TTF1-negative non-small cell lung cancer (NSCLC), TTF1-positive NSCLC, intrahepatic cholangiocarcinoma, ovarian cancer, renal cell carcinoma, salivary gland carcinoma, and breast cancer. The gene discussed is TTF1; the disease is ovarian carcinoma.