However, the CHEK2 1100delC mutation has not only been suggested to act as a low-penetrant susceptibility gene in breast cancer families, but the CHEK2 I157T alteration has been proposed to act as a multiorgan cancer susceptibility allele based on observations of an increased risk for development of breast cancer, colon cancer, prostate cancer, thyroid cancer, and renal cancer in Polish families [23]. This evidence concerns the gene CHEK2 and thyroid cancer.