Somatic ATF4 copy number loss associated with decreased protein levels in primary medullary thyroid carcinomas (MTC). A. Copy number variation analysis of MTC tumors using real-time polymerase chain reaction and CopyCaller Software V2.0 (n=59). The top plot displays the calculated copy number of each sample, and bars indicate the minimum and maximum copy number (CN) calculated for the sample replicate group. The bottom plot displays the predicted copy number. B. Immunohistochemical analysis of ATF4, Hematoxylin, and eosin staining in primary MTCs. The representative of ATF4 staining of primary tumors with 0 copy, one copy loss, two copies, a case with 2.5 ATF4 copies, and corresponding H&E staining. A negative control (spleen tissue) and positive control (normal thyroid) for ATF4 are shown.