Editing Breast (section)

==Development==
{{Main|Breast development}}

The breasts are principally composed of adipose, [[glandular tissue|glandular]], and [[w:connective tissue|connective]] tissues.<ref name="yen">{{citation |title = Yen & Jaffe's Reproductive Endocrinology |url = https://www.elsevier.com/books/yen-and-jaffes-reproductive-endocrinology/strauss/978-1-4160-4907-4 |author = Robert L. Barbieri |doi = 10.1016/B978-1-4160-4907-4.00010-3 |edition = 6th |publisher = Elsevier |date = 2009 |journal = Yen |pages = 235–248 |isbn = 978-1-4160-4907-4 |access-date = 6 March 2018 |archive-url = https://web.archive.org/web/20180306142739/https://www.elsevier.com/books/yen-and-jaffes-reproductive-endocrinology/strauss/978-1-4160-4907-4 |archive-date = 6 March 2018 |url-status = live |df = dmy-all |url-access = subscription }}
</ref> Because these tissues have hormone receptors,<ref name="yen" /><ref name="gland activation">{{citation |title = Hormone Action in the Mammary Gland |author1 = Brisken |author2 = Malley |doi = 10.1101/cshperspect.a003178 |date = 2 December 2010 |pmid = 20739412 |pmc = 2982168 |volume = 2 |issue = 12 |journal = Cold Spring Harb Perspect Biol |pages = a003178 }}</ref> their sizes and volumes fluctuate according to the hormonal changes particular to thelarche (sprouting of breasts), menstruation (egg production), pregnancy (reproduction), lactation (feeding of offspring), and menopause (end of menstruation).

===Puberty===
[[File:Female breasts five Tanner stages.jpg|thumb|Breast development in puberty is measured with the five-stage Tanner scale]]

The morphological structure of the human breast is identical in males and females until [[puberty]]. For pubescent girls in thelarche (the breast-development stage), the female [[sex hormone]]s (principally estrogens) in conjunction with [[growth hormone]] promote the sprouting, growth, and development of the breasts. During this time, the mammary glands grow in size and volume and begin resting on the chest. These development stages of [[secondary sex characteristic]]s (breasts, pubic hair, etc.) are illustrated in the five-stage [[Tanner scale]].<ref name="A.R.Greenbaum">{{cite journal |vauthors = Greenbaum AR, Heslop T, Morris J, Dunn KW |title = An Investigation of the Suitability of Bra fit in Women Referred for Reduction Mammaplasty |journal = British Journal of Plastic Surgery |volume = 56 |issue = 3 |pages = 230–6 |date = April 2003 |pmid = 12859918 |doi = 10.1016/S0007-1226(03)00122-X }}</ref>

During [[thelarche]], the developing breasts are sometimes of unequal size, and usually the left breast is slightly larger. This condition of asymmetry is transitory and statistically normal in female physical and sexual development.<ref name="asymmetry">{{cite journal |author = Loughry CW |title = Breast Volume Measurement of 598 Women using Biostereometric Analysis |journal = Annals of Plastic Surgery |year = 1989 |volume = 22 |issue = 5 |pages = 380–385 |doi = 10.1097/00000637-198905000-00002 |pmid = 2729845 |display-authors = 1 |last2 = Sheffer |first2 = Daniel B. |last3 = Price |first3 = Thomas E. |last4 = Einsporn |first4 = Richard L. |last5 = Bartfai |first5 = Ronald G. |last6 = Morek |first6 = Wayne M. |last7 = Meli |first7 = Nancy M. |s2cid = 8713713 }}</ref> Medical conditions can cause overdevelopment (e.g., virginal breast hypertrophy, [[macromastia]]) or underdevelopment (e.g., [[tuberous breast deformity]], [[micromastia]]) in girls and women.

Approximately two years after the onset of puberty (a girl's first [[menstrual cycle]]), estrogen and growth hormone stimulate the development and growth of the glandular fat and suspensory tissues that compose the breast. This continues for approximately four years until the final shape of the breast (size, volume, density) is established at about the age of 21. [[Mammoplasia]] (breast enlargement) in girls begins at puberty, unlike all other primates, in which breasts enlarge only during lactation.<ref name="stoppler" />

=== Hormone replacement therapy ===
[[File:Transsexual HRT induced developed breasts.jpg|thumb|upright|A transgender woman with HRT-induced developed breasts.]]
[[Hormone replacement therapy]], including [[gender-affirming hormone therapy]], stimulates the growth of glandular and adipose tissue through estrogen supplementation.<ref>{{Cite journal |last1=De |first1=Blok Christel |last2=Klaver |first2=Maartje |last3=Nota |first3=Nienke |last4=Dekker |first4=Marieke |last5=Den |first5=Heijer Martin |date=2016-05-13 |title=Breast development in male-to-female transgender patients after one year cross-sex hormonal treatment |url=https://www.endocrine-abstracts.org/ea/0041/ea0041gp146 |journal=Endocrine Abstracts |language=en |volume=41 |doi=10.1530/endoabs.41.GP146 |issn=1470-3947|url-access=subscription }}</ref>

In menopausal women, HRT helps restore breast volume and skin elasticity diminished by declining estrogen levels, typically using oral or transdermal estradiol.<ref>{{Cite journal |title=Postmenopausal Hormone Therapy: An Endocrine Society Scientific Statement |date=2010 |pmc=6287288 |last1=Santen |first1=R. J. |last2=Allred |first2=D. C. |last3=Ardoin |first3=S. P. |last4=Archer |first4=D. F. |last5=Boyd |first5=N. |last6=Braunstein |first6=G. D. |last7=Burger |first7=H. G. |last8=Colditz |first8=G. A. |last9=Davis |first9=S. R. |last10=Gambacciani |first10=M. |last11=Gower |first11=B. A. |last12=Henderson |first12=V. W. |last13=Jarjour |first13=W. N. |last14=Karas |first14=R. H. |last15=Kleerekoper |first15=M. |last16=Lobo |first16=R. A. |last17=Manson |first17=J. E. |last18=Marsden |first18=J. |last19=Martin |first19=K. A. |last20=Martin |first20=L. |last21=Pinkerton |first21=J. V. |last22=Rubinow |first22=D. R. |last23=Teede |first23=H. |last24=Thiboutot |first24=D. M. |last25=Utian |first25=W. H. |author26=Endocrine Society |journal=The Journal of Clinical Endocrinology and Metabolism |volume=95 |issue=7 Suppl 1 |pages=s1–s66 |doi=10.1210/jc.2009-2509 |pmid=20566620 }}</ref>

In gender-affirming hormone therapy, breast development is induced through feminizing HRT, often combining estrogen with anti-androgens to suppress testosterone. Maximum growth is usually achieved after 2–3 years.<ref>{{Cite web |title=Information on Estrogen Hormone Therapy {{!}} Gender Affirming Health Program |url=https://transcare.ucsf.edu/article/information-estrogen-hormone-therapy |access-date=2024-12-02 |website=transcare.ucsf.edu}}</ref><ref>{{Cite web |title=Practical Guidelines for Transgender Hormone Treatment {{!}} Endocrinology, Diabetes, Nutrition & Weight Management |url=https://www.bumc.bu.edu/endo/clinics/transgender-medicine/guidelines/ |access-date=2024-12-02 |website=www.bumc.bu.edu}}</ref><ref>{{Cite web |title=Transgender and Gender Diverse Hormone Therapy |url=https://www.hopkinsmedicine.org/-/media/center-for-transgender-health/documents/tgd-gaht-quick-guide.ashx |website=hopkinsmedicine.org}}</ref>

Factors such as age, genetics, and hormone dosage influence outcomes.

===Changes during the menstrual cycle===
During the menstrual cycle, the breasts are enlarged by [[premenstrual water retention]] and temporary growth as influenced by changing hormone levels.<ref name="mlpswelling">{{citation |title = Breast – premenstrual tenderness and swelling |url = https://www.nlm.nih.gov/medlineplus/ency/article/003153.htm |publisher = A.D.A.M. |date = May 2012 |access-date = 21 March 2018 |archive-url = https://web.archive.org/web/20160705060104/https://www.nlm.nih.gov/medlineplus/ency/article/003153.htm |archive-date = 5 July 2016 |url-status = live |df = dmy-all }}
</ref> 
===Pregnancy and breastfeeding===
{{Main articles|Maternal physiological changes in pregnancy|Breastfeeding}}
[[File:Breasts_with_visible_veins_on_surface.png|thumb|Postpartum breasts showing veins visible on surface]]
The breasts reach full maturity only when a woman's first pregnancy occurs.{{sfn | Lawrence | 2016 | p=34}}  Changes to the breasts are among the first signs of pregnancy. The breasts become larger, the nipple-areola complex becomes larger and darker, the [[Montgomery's glands]] enlarge, and veins sometimes become more visible. Breast tenderness during pregnancy is common, especially during the first trimester. By mid-pregnancy, the breast is physiologically capable of lactation and some women can express [[colostrum]], a form of breast milk.{{sfn | Lawrence | 2016 | p=58}}

Pregnancy causes elevated levels of the hormone [[prolactin]], which has a key role in the production of milk. However, milk production is blocked by the hormones [[progesterone]] and [[estrogen]] until after delivery, when progesterone and estrogen levels plummet.<ref name="NCBI Bookshelf 2008"/>

===Menopause===
[[File:Stretch marks on female breast.jpg|thumb|left|Breast with visible [[stretch marks]]]]{{Main article|Menopause}}
At menopause, breast atrophy occurs.<ref>{{Cite journal |title=Menopausal Transition, Body Mass Index, and Prevalence of Mammographic Dense Breasts in Middle-Aged Women |date=2020 |pmc=7465213 |last1=Kim |first1=E. Y. |last2=Chang |first2=Y. |last3=Ahn |first3=J. |last4=Yun |first4=J. S. |last5=Park |first5=Y. L. |last6=Park |first6=C. H. |last7=Shin |first7=H. |last8=Ryu |first8=S. |journal=Journal of Clinical Medicine |volume=9 |issue=8 |page=2434 |doi=10.3390/jcm9082434 |doi-access=free |pmid=32751482 }}</ref> The breasts can decrease in size when the levels of circulating estrogen decline. The adipose tissue and milk glands also begin to wither. The breasts can also become enlarged from [[Adverse effect|adverse side effects]] of [[combined oral contraceptive pill]]s. The size of the breasts can also increase and decrease in response to [[body weight|weight]] fluctuations.<ref>{{Cite journal |last1=Wanders |first1=Johanna Olga Pauline |last2=Bakker |first2=Marije Fokje |last3=Veldhuis |first3=Wouter Bernard |last4=Peeters |first4=Petra Huberdina Maria |last5=van Gils |first5=Carla Henrica |date=2015-05-30 |title=The effect of weight change on changes in breast density measures over menopause in a breast cancer screening cohort |journal=Breast Cancer Research |volume=17 |issue=1 |pages=74 |doi=10.1186/s13058-015-0583-2 |doi-access=free |issn=1465-542X |pmc=4487974 |pmid=26025139}}</ref> 

Physical changes to the breasts are often recorded in the [[stretch marks]] of the skin envelope; they can serve as historical indicators of the increments and the decrements of the size and volume of a woman's breasts throughout the course of her life.{{Verification needed|date=December 2024|reason=This statement may not correspond to present sources}}

Breast changes during menopause are sometimes treated with [[hormone replacement therapy]].<ref>{{Cite web |date=2023-02-07 |title=What You Should Know About Hormone Therapy and Menopause |url=https://www.cuimc.columbia.edu/news/what-you-should-know-about-hormone-therapy-and-menopause |access-date=2024-12-25 |website=Columbia University Irving Medical Center |language=en}}</ref>

===Cancer===
{{Main|Breast cancer}}
Breast cancer is a cancer that develops from breast tissue.<ref>{{cite web |title = Breast Cancer |url = http://www.cancer.gov/cancertopics/types/breast |website = NCI |access-date = 29 June 2014 |url-status = live |archive-url = https://web.archive.org/web/20140625232947/http://www.cancer.gov/cancertopics/types/breast |archive-date = 25 June 2014 |date = January 1980 }}</ref> Signs of breast cancer may include a [[Breast lump|lump]] in the breast, a change in breast shape, [[dimpling]] of the skin, [[Milk-rejection sign|milk rejection]], fluid coming from the [[nipple]], a newly inverted nipple, or a red or scaly patch of skin.<ref name=NCI2014Pt>{{cite web |title = Breast Cancer Treatment (PDQ®) |url = http://www.cancer.gov/cancertopics/pdq/treatment/breast/Patient/page1/AllPages |website = NCI |date = 23 May 2014 |access-date = 29 June 2014 |url-status = live |archive-url = https://web.archive.org/web/20140705110404/http://www.cancer.gov/cancertopics/pdq/treatment/breast/Patient/page1/AllPages |archive-date = 5 July 2014 }}</ref> In those with [[Metastatic breast cancer|distant spread of the disease]], there may be [[bone pain]], swollen [[lymph node]]s, [[shortness of breath]], or [[yellow skin]].<ref>{{cite book | vauthors = Saunders C, Jassal S |title = Breast cancer |date = 2009 |publisher = Oxford University Press |location = Oxford |isbn = 978-0-19-955869-8 |page = Chapter 13 |edition = 1. |url = https://books.google.com/books?id=as46WowY_usC&pg=PT123 |url-status = live |archive-url = https://web.archive.org/web/20151025013217/https://books.google.com/books?id=as46WowY_usC&pg=PT123 |archive-date = 25 October 2015 }}</ref>

Risk factors for developing breast cancer include [[obesity]], a [[Sedentary lifestyle|lack of physical exercise]], alcohol consumption, [[hormone replacement therapy]] during [[menopause]], [[ionizing radiation]], an early age at [[Menarche|first menstruation]], having children late in life (or not at all), older age, having a prior history of breast cancer, and a family history of breast cancer.<ref name=NCI2014Pt /><ref name="WCR2014">{{cite book |title = World Cancer Report 2014 |date = 2014 |publisher = World Health Organization |isbn = 978-92-832-0429-9 |pages = Chapter 5.2 }}</ref><ref>{{cite journal | vauthors = Fakhri N, Chad MA, Lahkim M, Houari A, Dehbi H, Belmouden A, El Kadmiri N | title = Risk factors for breast cancer in women: an update review | journal = Medical Oncology | volume = 39 | issue = 12 | pages = 197 | date = September 2022 | pmid = 36071255 | doi = 10.1007/s12032-022-01804-x | s2cid = 252113509 }}</ref> About five to ten percent of cases are the result of an inherited genetic predisposition,<ref name=NCI2014Pt /> including [[BRCA mutation|''BRCA'' mutations]] among others.<ref name=NCI2014Pt /> Breast cancer most commonly develops in cells from the lining of [[milk ducts]] and the [[lobules]] that supply these ducts with milk.<ref name=NCI2014Pt /> Cancers developing from the ducts are known as [[Invasive ductal carcinoma|ductal carcinomas]], while those developing from lobules are known as [[lobular carcinoma]]s.<ref name=NCI2014Pt /> There are more than 18 other sub-types of breast cancer.<ref name=WCR2014 /> Some, such as [[ductal carcinoma in situ]], develop from [[pre-invasive lesions]].<ref name=WCR2014 /> The diagnosis of breast cancer is confirmed by taking a [[Breast biopsy|biopsy]] of the concerning tissue.<ref name=NCI2014Pt /> Once the diagnosis is made, further tests are carried out to determine if the cancer has spread beyond the breast and which treatments are most likely to be effective.<ref name=NCI2014Pt />