To test this hypothesis, we analyzed the expression of PRL3, γH2AX, and Chk2 in four pairs of post-chemotherapy primary tumors and patient-matched metastatic or recurrent tumors; Pair 1: breast invasive carcinoma sample, and its metastatic tumor in the brain; pair 2: colon adenocarcinoma sample and its metastatic tumor in the liver; pair 3: rectal cancer sample and its metastatic tumor in the lung and pair 4: thyroid cancer sample and its recurrent thyroid tumor. The gene discussed is CHEK2; the disease is thyroid cancer.