Quote from "Pediatric Surgery (Springer Surgery Atlas)" by Prem Puri, Michael E. Höllwarth - "The breast tissue present in gynecomastia is most often tender, firm, and subareolar. One third of boys will present with unilateral gynecomastia. A mass in the breast that is not subareolar and is asymmetric should raise concern for other conditions. A testicular exam is a key component of the physical exam to rule out hypogonadism, suggestive of Klinefelter’s syndrome, a varicocele, or possible estrogen-secreting tumors of the testes, such as germ cell tumors, Sertoli cell tumors, or Leydig cell tumors."