STK11 and breast cancer: Many studies have revealed that breast cancer is caused by environmental factors, such as obesity [3], heavy smoking [4], and genetic factors such as breast cancer gene (BRCA)1, BRCA2, phosphatase and tensin homolog (PTEN), tumor protein P53 (TP53), cadherin 1 (CDH1), and serine/threonine kinase 11 (STK11) [5].