Conventional biopsy consists of histological (visual identification of cancerous cells), immunohistochemical (expression of TTF1, p40 or p63, CK5/6, napsin or CK7, PD-L1 (LC) and MLH1, MSH2, MSH6, and PMS2 (CRC)), and genetic (search for mutations in EGFR, ALK, ROS-1 genes (LC) and in KRAS, NRAS, BRAF, PIK3CA, PTEN genes (CRC); CIN and CIMP status, microsatellite instability (MSI) status (CRC) associated with the response to targeted therapy) analyses of a tissue sample obtained by an invasive method [8,9]. The gene discussed is MLH1; the disease is colorectal carcinoma.