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Gyne refers to female, and mastia refers to the breast. Gynecomastia is strictly a male disease and is any growth of the adipose (fatty) and glandular tissue in a male breast. Not all breast growth in men is considered abnormal, just excess growth.

Causes and symptoms

Breast growth is directed exclusively by female hormones—estrogens. Although men have some estrogen in their system, it is usually insufficient to cause much breast enlargement because it is counterbalanced by male hormones—androgens. Upsetting the balance, either by more of one or less of the other, results in the male developing female characteristics, breast growth being foremost.
At birth both male and female infants will have little breast buds from their mother's hormones. These recede until adolescence, when girls always, and boys sometimes, have breast growth. At this time, the boy's breast growth is minimal, often one-sided and temporary.
Extra or altered sex chromosomes can produce intersex problems of several kinds. Breast growth along with male genital development is seen in Klinefelter syndrome—the condition of having an extra X (female) chromosome—and a few other chromosomal anomalies. One of the several glands that produce hormones can malfunction for reasons other than chromosomes. Failure of androgen production is as likely to produce gynecomastia as overabundant estrogen production. Testicular failure and castration can also be a cause. Some cancers and some benign tumors can make estrogens. Lung cancer is known to increase estrogens.
If the hormone manufacturing organs are functioning properly, problems can still arise elsewhere. The liver is the principle chemical factory in the body. Other organs like the thyroid and kidneys also effect chemical processes. If any of these organs are diseased, a chemical imbalance can result that alters the manufacturing process. Men with cirrhosis of the liver will often develop gynecomastia from increased production of estrogens.
Finally, drugs can also cause breast enlargement. Estrogens are given to men to treat prostate cancer and a few other diseases. Marijuana and heroin, along with some prescription drugs, have estrogen effects in some men. On the list are methyldopa (for blood pressure), cimetidine (for peptic ulcers), diazepam (Valium), antidepressants, and spironolactone (a diuretic).


Carefully feeling the area beneath the nipple of an adolescent boy with breast enlargement will reveal a discreet and sometimes tender lump the size of a fat nickel or quarter. For more serious gynecomastia, the underlying disease will require evaluation, if it is not already well understood.

Key terms

Androgen — Male sex hormone.
Cirrhosis — Diffuse scarring caused by alcohol or chronic hepatitis often leading to liver failure.
Estrogen — Sex hormone responsible for stimulating female sexual characteristics.
Klinefelter syndrome — A condition in a male characterized by having an extra X (female) chromosome and suffering from infertility and gynecomastia.
Thyroid — A gland in the neck that makes thyroxin. Thyroxin regulates the speed of metabolism.


This condition is usually not treated. If it is the result of endocrine disease, hormone manipulations may reduce the effects of the imbalance. There are a number of medical and surgical interventions possible. Radiation of misbehaving organs and cancers is considered an effective treatment.


The progress of gynecomastia is determined by its cause.



Wilson, Jean D. "Endocrine Disorders of the Breast." In Harrison's Principles of Internal Medicine, edited by Anthony S. Fauci, et al. New York: McGraw-Hill, 1997.
Gale Encyclopedia of Medicine. Copyright 2008 The Gale Group, Inc. All rights reserved.


 [gi″nĕ-] , [jin″ĕ-ko-mas´te-ah]
enlargement of one or both breasts in a male, usually seen in adolescents or elderly men due to excessive estrogen activity; occasionally there is even excretion of milk.
Miller-Keane Encyclopedia and Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition. © 2003 by Saunders, an imprint of Elsevier, Inc. All rights reserved.


, gynecomasty (gī'nĕ-kō-mas'tē-ă, jin'ĕ-; -mas'tē), Although the first syllable of this word is correctly pronounced jīn, it is often pronounced gīn, gĭn, or jĭn.
Excessive development of the male mammary glands, due mainly to ductal proliferation with periductal edema; frequently secondary to increased estrogen levels, but mild gynecomastia may occur in normal adolescence.
[gyneco- + G. mastos, breast]
Farlex Partner Medical Dictionary © Farlex 2012


(gī′nĭ-kō-măs′tē-ə, jĭn′ĭ)
Abnormal enlargement of the breasts in a male.
The American Heritage® Medical Dictionary Copyright © 2007, 2004 by Houghton Mifflin Company. Published by Houghton Mifflin Company. All rights reserved.


Benign enlargement of ♂ breast that most commonly affects boys and adolescents, often regresses at puberty; it is usually due to a proliferation of glandular component; may occur in Klinefelter syndrome or after malnutrition Age-related peaks
1. Perinatal, in 60-90% of ♂ at birth, due to transplacental passage of estrogens.
2. Pubertal, up to 70%, depending on stringency of definition.
3. Involutional, age 50-80% Treatment Clomiphene, tamoxifen, testolactone, surgery. See Adolescent gynecomastia.
Gynecomastia Etiology
Endocrinopathy Orchitis, hypogonadism–androgen deficiency, androgen resistance, tumors/hyperplasia of adrenal gland, testes, eg Leydig cell tumor–↑ hCG, lung CA, Klinefelter syndrome–↑ risk of breast CA and thyroid hyperplasia
Drugs α-methyldopa, amphetamine, androgens, benzodiazepines, cimetidine, chemotherapeutics, digitalis, INH, marijuana, penicillamine, phenothiazine, reserpine, spironolactone, tricyclic antidepressants
Other conditions Starvation diet–mechanism: testicular, hepatic hypofunction or on resuming feeding, hemodialysis, liver disease–cirrhosis, hepatomas, hemochromatosis, due to ↓ hepatic metabolism of estrogens, mycosis fungoides, myotonic dystrophy with spastic paraplegia, leprosy
McGraw-Hill Concise Dictionary of Modern Medicine. © 2002 by The McGraw-Hill Companies, Inc.


, gynecomasty (gī'nĕ-kō-mas'tē-ă, -mas'tē)
Excessive development of the male mammary glands, due mainly to ductal proliferation with periductal edema; frequently secondary to increased estrogen levels, but mild gynecomastia may occur in normal adolescents.
Synonym(s): gynaecomastia, gynaecomasty.
[gyneco- + G. mastos, breast]
Medical Dictionary for the Health Professions and Nursing © Farlex 2012


(jī″nĕ-kō-mas′tē-ă, gī″, jĭn″ĕ-) [ gyneco- + masto- + -ia]
Enlarge picture
Enlargement of breast tissue in the male. This may occur during three distinct age periods: transiently at birth, again beginning with puberty and declining during the late teenage years, and finally in adults over age 50 years. In the newborn, it is caused by stimulation from maternal hormones. A milky secretion (“witch's milk”) may be produced; the condition disappears within a few weeks. During middle adolescence, as many as 60% of boys may develop some degree of gynecomastia, either unilateral or bilateral and, if bilateral, often with varying degrees of growth between the two sides. It may be produced by the use of alcohol, marijuana, and heroin, but it is often a normal, nonpathological condition and usually disappears within 18 months. Hormonal assays should be performed only if the condition appears before puberty, persists longer than 2 years, or is associated with other signs of endocrine disorders. In older men, the condition can be caused by pituitary or testicular tumors, medications such as spironolactone or antiandrogens, or cirrhosis of the liver causing enhanced activity (due to delayed liver catabolism) of naturally produced estrogens. See: illustration


Therapy depends on the cause. Because gynecomastia has a high rate of spontaneous regression, medical therapies are most effective during the active proliferative phase. To help alleviate the acute embarrassment from the condition adolescent boys may suffer, they should be reassured that the problem will go away. Tender breasts should be treated with analgesics.

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