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Breast cancer is when cancer develops from breast tissue.[1] Signs of breast cancer may include: a lump in the breast, a change in the breasts shape, dimpling of the skin, fluid coming from the nipple, or a red scaly patch of skin.[2] In those with distant spread of the disease, there may be bone pain, swollen lymph nodes, shortness of breath or yellow skin.[3]
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’’’乳癌’’’（{{lang-en|breast cancer}}）是由[[乳房]]組織發展成的[[癌症]][1]。乳癌的徵象包括乳房腫塊、乳房形狀改變、皮膚[[酒窩|凹陷]]、乳頭分泌物或是皮膚出現紅色鱗屑狀斑塊[2]。而出現遠端轉移的病患，可能會有{{link-en|骨痛|Bone pain}}、[[淋巴結]]腫大、[[呼吸困難]]或[[黃疸]]的情形[3]。
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Risk factors include: obesity, lack of physical exercise, drinking alcohol, hormone replacement therapyduring menopause, ionizing radiation, early age at firstmenstruation and having children late or not at all.[2][4]About 5-10% of cases are due to genes inherited from a person’s parents. These include BRCA1 and BRCA2 among others. Breast cancer occurs most commonly from the lining of milk ducts or the lobules that supply the ducts with milk. Cancer from the ducts is known asductal carcinomas, while those from lobules are known as lobular carcinomas.[2] In addition there are more than 18 other sub-types. Some cancers develop from pre-invasive lesions such as ductal carcinoma in situ.[4] The diagnosis is confirmed by taking a biopsy of the concerning lump. Once the diagnosis is made further tests are done to determine if the cancer has spread and what treatments it may respond to.[2]
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乳癌的風險因子包含了：[[肥胖症]]、缺乏運動、飲[[醇|酒]]、[[更年期]]時的{{link-en|激素替代療法|Hormone replacement therapy}}、[[游離輻射]]、[[月經|初經]]提早開始與晚生或不生育[2][4]。大約5至10%的病例是因父母親的[[遺傳]]而發生。這些遺傳因子包含了{{link-en|BRCA1|BRCA1}}、{{link-en|BRCA2|BRCA2}}與其他因子。乳癌最常發生於供應母乳的{{link-en|乳腺|Lactiferous duct}}或{{link-en|乳葉|Lobe (anatomy)}}內側。如果發生在乳腺，則稱做{{link-en|非特殊型侵襲性導管癌|ductal carcinoma|乳腺癌}}，發生在乳葉的則稱為{{link-en|乳葉癌|Lobular carcinoma}}[2]。此外，乳癌還分成18個子類型。部分乳癌會先從{{link-en|癌前狀態|Precancerous condition}}開始發展，例如{{link-en|原位導管癌|Ductal carcinoma in situ}}[4]。診斷方面，通常會針對腫瘤進行[[活體組織切片]]來確診。如果確診，就會進行進一步檢測，確認乳癌是否發生擴散與治療方式[2]。
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The balance of benefits versus harms of breast cancer screening is controversial. A 2013 Cochrane review stated that it is unclear if mammographic screening does more good or harm.[5] A 2009 review for the US Preventive Services Task Force found evidence of benefit in those 40 to 70 years of age,[6] and the organization recommends screening every two years in women 50 to 74 years old.[7] In those who are at high risk the medications tamoxifen or raloxifene may be used in an effort to prevent cancer.[4] Surgical removal of both breasts is another useful preventative measure in some high risk women.[4] In those who have cancer a number of treatments may be used including: surgery, radiation therapy, chemotherapy, and targeted therapy.[2] Types of surgery vary from breast-conserving surgery to mastectomy.[8][9] Breast reconstruction may take place at the time or surgery or at a later date. In those in whom the cancer has spread to other parts of the body treatments are aimed at improving quality of life and comfort.[9]
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{{link-en|乳腺癌篩檢|Breast cancer screening}}究竟是否有益仍具有爭議性。2013年{{linke-en|考科藍合作組織|Cochrane Collaboration}}的評論，認為[[乳房攝影術]]是否有益還是有害，目前還不清楚。2009年，{{link-en|美國預防服務工作組|United States Preventive Services Task Force}}的評論認為，有證據顯示乳房攝影術對於40至70歲的婦女有益，並建議50至74歲的婦女每兩年檢驗一次。對於有高風險的人，{{link-en|太莫西芬|Tamoxifen}}或{{link-en|雷洛昔芬|Raloxifene}}等藥物可用於預防乳癌發生。{{link-en|預防性乳房切除術|Preventive mastectomy}}也是部分高風險婦女可以採用的預防措施。如果得到乳癌，會使用數種治療方式，包含：[[外科學|手術]]、[[放射線療法]]、[[化學療法]]與[[標靶治療]]。乳癌手術的種類，從{{link-en|乳房保留手術|Breast-conserving surgery}}到[[乳房切除術]]，有不同的手術方式。在手術當下或數日之後，可能會進行[[乳房重建]]。若乳癌中的癌細胞已擴散到其他身體部位的病患，則改以提高生活品質而非積極治療為主要的目標。
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Outcomes for breast cancer vary depending on the cancer type, extent of disease, and person’s age.[9] Survival rates in the developed world are high;[10] with between 80% and 90% of those in England and the United States alive for at least 5 years.[11][12] In developing countries survival rates are poorer.[4] Worldwide, breast cancer is the leading type of cancer in women, accounting for 25% of all cases.[13] In 2012 it resulted in 1.68 million cases and 522,000 deaths.[13]It is more common in developed countries[4] and is more than 100 times more common in women than in men.[10][14]
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乳癌的預後依癌症的類型、{{link-en|癌症分期|Cancer staging}}以及病患年紀有所不同。在[[已開發國家]]中，病患的存活率較高；在英國和美國，{{link-en|五年存活率|Five-year survival rate}}可達八成到九成。在開發生國家中，存活率則稍差。以全球而言，乳癌是女性癌症中最常見的，佔了25%，在2012年，有168萬的乳癌個案，及52萬人因乳癌死亡。乳癌在已開發國家較常見，且女性患乳癌的機率是男性的100倍。