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Received Dec 13, 2017; Revised Apr 17, 2018; Accepted Apr 26, 2018
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1. Introduction
Gynecomastia, defined as the benign proliferation of breast glands in males, is a common complaint that produces anxiety and discomfort and it may be the expression of a clinically relevant disease [1, 2].
Gynecomastia may be diagnosed on routine clinical examination or patients may present with complaints of a retroareolar nodule. This condition may occur sporadically or in a familial setting, and it may be unilateral or bilateral, painful or painless, of acute onset or progressive growth [3–5].
The hormones involved in breast tissue physiology may be stimulatory (as estradiol and progesterone) or inhibitory (as testosterone), acting directly through their specific receptors at this level [6, 7]. Receptors for insulin-like growth factor 1 (IGF-1), IGF-2 [8], luteinizing hormone, and human chorionic gonadotropin have also been detected in breast tissue [7, 8]. Estrogens and progesterone apparently require the presence of growth hormone and IGF-1 to exert their stimulatory action on the breast [9]. Hyperprolactinemia may indirectly cause gynecomastia by suppressing gonadotropin-releasing hormone (GnRH) release, resulting in central hypogonadism, although prolactin receptors have also been detected in benign and malignant breast tissue. At breast level, prolactin might modulate progesterone and androgen receptors expression (increasing the former and reducing the latter) [10]. Furthermore, prolactin stimulates epithelial cell proliferation only in the presence of estrogen and enhances lobuloalveolar differentiation only with concomitant progesterone [7].
Gynecomastia may result from an excess of estrogens (obesity, tumors, and exogenous sources) [11], androgen deficiency (hypogonadism), hormone resistance [12], or altered ratio of estrogens to androgens (refeeding, liver disease, and renal failure) [13].
It may also be a physiological phenomenon in different stages of life, such as in the newborn, during pubertal development [14], and in the elderly [15, 16], or it may be a pathological condition caused by drugs of abuse [17, 18], systemic disease [17, 19], endocrine disorders, tumors, and medications [17]. Even though gynecomastia is a common condition, e.g., palpable breast tissue may be detected in one- to two-thirds of adult males, while autopsy data suggest a...