The changes in fibrocystic breast disease are characterised by the appearance of fibrous tissue and a lumpy, cobblestone texture in the breasts. These lumps are smooth with defined edges, and are usually free-moving in regard to adjacent structures. The bumps can sometimes be obscured by irregularities in the breast that are associated with the condition. The lumps are most often found in the upper, outer sections of the breast (nearest to the armpit), but can be found throughout the breast. Women with fibrocystic changes may experience a persistent or intermittent breast aching or breast tenderness related to periodic swelling. Breasts and nipples may be tender or itchy.

Symptoms follow a periodic trend tied closely to the menstrual cycle. Symptoms tend to peak in the days and, in severe cases, weeks before each period and decrease afterwards. At peak, breasts may feel full, heavy, swollen, and tender to the touch. No complications related to breastfeeding have been found.

In ICD-10 the condition is called "diffuse cystic mastopathy", or, if there is epithelial proliferation, "fibrosclerosis of breast". Other names for this condition include "chronic cystic mastitis", "fibrocystic mastopathy" and "mammary dysplasia". The condition has also been named after several people (see eponyms below). Since it is a very common disorder, some authors have argued that it should not be termed a "disease", whereas others feel that it meets the criteria for a disease. It is not a classic form of mastitis (breast inflammation).

Symptoms are very variable and may not be present at all in "occult inflammatory breast cancer". Quick onset of symptoms is typical, the breast often looks swollen and red, or “inflamed”, sometimes overnight, and are easy to misdiagnose as mastitis. Invasion of the local lymphatic ducts impairs drainage and causes edematous swelling of the breast. Because the skin of the breast is tethered by the suspensory ligament of Cooper, the accumulation of fluid may cause the skin of the breast to assume a dimpled appearance similar to an orange peel (peau d'orange). A palpable tumor is frequently not obvious as in other forms of breast cancer.

Symptoms may include:

- Sudden swelling of the breast

- Skin changes on breast

- Reddened area with texture resembling the peel of an orange (peau d’orange)

- Nipple retraction (flattened look) or discharge

- Pain in the breast

- Itching of breast

- Swelling of lymph nodes under the arm or in the neck

- Unusual warmth of the affected breast

- Breast is harder or firmer

Other symptoms may rarely include:

- Swelling of the arm

- Breast size may decrease instead of increasing

- Although a dominant mass is present in many cases, most inflammatory cancers present as diffuse infiltration of the breast without a well-defined tumor.

- A lump may become present and grow rapidly

Most patients do not experience all the symptoms of IBC. Not all symptoms need to be present in order to be diagnosed.

Breast diseases can be classified either with disorders of the integument, or disorders of the reproductive system. A majority of breast diseases are noncancerous.

Inflammatory breast cancer is one of the most aggressive types of breast cancer that can occur in women of any age (and,

extremely rarely, in men). It is called inflammatory because it frequently presents with symptoms resembling an inflammation. Despite the name, whether inflammation contributes to the development of "inflammatory breast cancer" remains an area of ongoing research. However it can present with very variable signs and symptoms, frequently without detectable tumors and therefore is often not detected by mammography or ultrasound.

Typical presentation is rapid swelling, sometimes associated by skin changes (peau d'orange), and nipple retraction. Other symptoms include rapid increase in breast size, redness, persistent itching, skin hot to touch. IBC often initially resembles mastitis.

Only about 50-75% cases have the typical presentation. Symptoms can be completely atypical such as acute central venous thrombosis as the sole presenting symptom.

IBC makes up only a small percentage of breast cancer cases (1-6% in the USA). IBC is often diagnosed in younger women although average age of presentation does not differ much from other kinds of breast cancer (average age 57 years). African-Americans are usually diagnosed at younger ages than Caucasian women, and also have a higher risk of getting IBC. Recent advances in therapy have improved the prognosis considerably and at least one third of women will survive the diagnosis by 10 years or longer.

Fibrosclerosis of the breast is most frequently used to mean sclerosing lobular adenosis of the breast. It is not well known if it is related to non-sclerosing adenosis of the breast (which is normally classified as fibrocystic breast changes) and unlike this it is believed to be correlated with an elevated risk of breast cancer.

Male breast cancer (male breast neoplasm) is a rare cancer in males that originates from the breast. Many males with breast cancer have inherited a "BRCA" mutation, but there are other causes, including alcohol abuse and exposure to certain hormones and ionizing radiation.

As it presents a similar pathology as female breast cancer, assessment and treatment relies on experiences and guidelines that have been developed in female patients. The optimal treatment is currently not known.

As in females, infiltrating ductal carcinoma is the most common type. While intraductal cancer, inflammatory carcinoma, and Paget's disease of the nipple have been described, lobular carcinoma in situ has not been seen in males. Breast cancer in males spreads via lymphatics and blood stream like female breast cancer. Accordingly, the TNM staging system for breast cancer is the same for males and females.

Size of the lesion and lymph node involvement determine prognosis; thus small lesions without lymph node involvement have the best prognosis. Estrogen receptor and progesterone receptor status and HER2/neu (Human Epidermal Growth Factor Receptor 2) gene amplification need to be reported as they may affect treatment options. About 85% of all male breast cancers are estrogen receptor–positive, and 70% are progesterone receptor–positive.

The first noticeable symptom of breast cancer is typically a lump that feels different from the rest of the breast tissue. More than 80% of breast cancer cases are discovered when the woman feels a lump. The earliest breast cancers are detected by a mammogram. Lumps found in lymph nodes located in the armpits can also indicate breast cancer.

Indications of breast cancer other than a lump may include thickening different from the other breast tissue, one breast becoming larger or lower, a nipple changing position or shape or becoming inverted, skin puckering or dimpling, a rash on or around a nipple, discharge from nipple/s, constant pain in part of the breast or armpit, and swelling beneath the armpit or around the collarbone. Pain ("mastodynia") is an unreliable tool in determining the presence or absence of breast cancer, but may be indicative of other breast health issues.

Inflammatory breast cancer is a particular type of breast cancer which can pose a substantial diagnostic challenge. Symptoms may resemble a breast inflammation and may include itching, pain, swelling, nipple inversion, warmth and redness throughout the breast, as well as an orange-peel texture to the skin referred to as "peau d'orange". As inflammatory breast cancer does not present as a lump there can sometimes be a delay in diagnosis.

Another reported symptom complex of breast cancer is Paget's disease of the breast. This syndrome presents as skin changes resembling eczema, such as redness, discoloration, or mild flaking of the nipple skin. As Paget's disease of the breast advances, symptoms may include tingling, itching, increased sensitivity, burning, and pain. There may also be discharge from the nipple. Approximately half of women diagnosed with Paget's disease of the breast also have a lump in the breast.

In rare cases, what initially appears as a fibroadenoma (hard, movable non-cancerous lump) could in fact be a phyllodes tumor. Phyllodes tumors are formed within the stroma (connective tissue) of the breast and contain glandular as well as stromal tissue. Phyllodes tumors are not staged in the usual sense; they are classified on the basis of their appearance under the microscope as benign, borderline, or malignant.

Occasionally, breast cancer presents as metastatic disease—that is, cancer that has spread beyond the original organ. The symptoms caused by metastatic breast cancer will depend on the location of metastasis. Common sites of metastasis include bone, liver, lung and brain. Unexplained weight loss can occasionally signal breast cancer, as can symptoms of fevers or chills. Bone or joint pains can sometimes be manifestations of metastatic breast cancer, as can jaundice or neurological symptoms. These symptoms are called "non-specific", meaning they could be manifestations of many other illnesses.

Most symptoms of breast disorders, including most lumps, do not turn out to represent underlying breast cancer. Fewer than 20% of lumps, for example, are cancerous, and benign breast diseases such as mastitis and fibroadenoma of the breast are more common causes of breast disorder symptoms. Nevertheless, the appearance of a new symptom should be taken seriously by both patients and their doctors, because of the possibility of an underlying breast cancer at almost any age.

Paget's disease of the breast can affect the nipple and areola. Symptoms typically only affect one breast. Symptoms may include:

- "Skin." The first symptom is usually an eczema-like rash. The skin of the nipple and areola may be red, itchy and inflamed. After a period of time, the skin may become flaky or scaly.

- "Discharge." A discharge, which may be straw-colored or bloody, may ooze from the area.

- "Sensation." Some women have a burning sensation. These symptoms usually occur in more advanced stages, when serious destruction of the skin often prompts the patient to consult. Lumps or masses in the breast occur in 50% of the patients. In more advanced stages, the disease may cause tingling, increased sensitivity and pain.

- Nipple changes. The nipple may turn inwards be inverted.

- Breast changes. There may or may not be a lump in the breast, and there may be redness, oozing and crusting, and a sore that does not heal.

The symptoms usually affect the nipple and then spread to the areola and then the breast. It is common for the symptoms to wax and wane.

Most women do not visit the doctor because they assume Paget's disease to be minor contact dermatitis or eczema. A lump or skin irritation that does not seem to heal for over a month indicates that attention by a specialist is needed.

Signs and symptoms of breast cysts include:

- A smooth, easily movable round or oval breast lump with distinct edges

- Breast pain or tenderness in the area of the lump

- Increased lump size and tenderness just before menstruation

- Decreased lump size and resolution of other signs and symptoms after menstruation

- Having one or many simple breast cysts does not increase a person's risk of breast cancer.

Lumps in the breast are often not found during self-examinations or physical exams. However, in some cases they can be felt at touch, especially if they are larger.

Breasts are usually lumpy or nodular as a result of the hormonal changes that women go through during their menstrual cycle. However, new breast lumps should always be referred to a specialist.

Fluid leaking from a cyst, as may happen due to puncture or vigorous compression during mammography, or due to seatbelt injury in the course of an automobile accident, may trigger an aseptic inflammation in the surrounding breast tissue.

Most of the women who develop DCIS do not experience any symptoms. The majority of cases (80-85%) are detected through screening mammography. The first signs and symptoms may appear if the cancer advances. Because of the lack of early symptoms, DCIS is most often detected at screening mammography.

In a few cases, DCIS may cause:

- A lump or thickening in or near the breast or under the arm

- A change in the size or shape of the breast

- Nipple discharge or nipple tenderness; the nipple may also be inverted, or pulled back into the breast

- Ridges or pitting of the breast; the skin may look like the skin of an orange

- A change in the way the skin of the breast, areola, or nipple looks or feels such as warmth, swelling, redness or scaliness.

A breast cyst is a fluid-filled sac within the breast. One breast can have one or more breast cysts. They are often described as round or oval lumps with distinct edges. In texture, a breast cyst usually feels like a soft grape or a water-filled balloon, but sometimes a breast cyst feels firm.

Breast cysts can be painful and may be worrisome but are generally benign. They are most common in pre-menopausal women in their 30s or 40s. They usually disappear after menopause, but may persist or reappear when using hormone therapy. They are also common in adolescents.

Breast cysts can be part of fibrocystic disease. The pain and swelling is usually worse in the second half of the menstrual cycle or during pregnancy.

Treating breast cysts is usually not necessary unless they are painful or cause discomfort. In most cases, the discomfort they cause may be alleviated by draining the fluid from the cyst. The cysts form as a result of the growth of the milk glands and their size may range from smaller than a pea to larger than a ping pong ball. Small cysts cannot be felt during a physical examination, and some large cysts feel like lumps. However, most cysts, regardless of their size cannot be identified during physical exams.

Breast cysts are not to be confused with "milk cysts" (galactoceles), which usually appear during weaning.

These may be caused among others by trauma, secretory stasis/milk engorgement, hormonal stimulation, infections or autoimmune reactions.

Repeated occurrence unrelated to lactation requires endocrinological examination.

- bacterial mastitis

- mastitis from milk engorgement or secretory stasis

- mastitis or mumps

- chronic subareolar abscess

- tuberculosis of the breast

- syphilis of the breast

- retromammary abscess

- actinomycosis of the breast

- duct ectasia syndrome

- breast engorgement

Triple-negative breast cancer (sometimes abbreviated TNBC) refers to any breast cancer that does not express the genes for estrogen receptor (ER), progesterone receptor (PR) or Her2/neu. This makes it more difficult to treat since most hormone therapies target one of the three receptors, so triple-negative cancers often require combination therapies. Triple negative is sometimes used as a surrogate term for basal-like; however, more detailed classification may provide better guidance for treatment and better estimates for prognosis.

Triple-negative breast cancers comprise a very heterogeneous group of cancers. There are conflicting information over prognosis for the various subtypes but it appears that the Nottingham prognostic index is valid and hence general prognosis is rather similar with other breast cancer of same stage, except that more aggressive treatment is required. Some types of triple-negative breast cancer are known to be more aggressive with poor prognosis, while other types have very similar or better prognosis than hormone receptor positive breast cancers. Pooled data of all triple-negative subtypes suggest that with optimal treatment 20-year survival rates are very close to those of hormone positive cancer.

Triple-negative breast cancers have a relapse pattern that is very different from hormone-positive breast cancers: the risk of relapse is much higher for the first 3–5 years but drops sharply and substantially below that of hormone-positive breast cancers after that. This relapse pattern has been recognized for all types of triple-negative cancers for which sufficient data exists although the absolute relapse and survival rates differ across subtypes.

Fibroadenomas, are benign breast tumours characterized by an admixture of stromal and epithelial tissue. Breasts are made of lobules (milk producing glands) and ducts (tubes that carry the milk to the nipple). These are surrounded by glandular, fibrous and fatty tissues. Fibroadenomas develop from the lobules. The glandular tissue and ducts grow over the lobule to form a solid lump.

Since both fibroadenomas, and breast lumps as a sign of breast cancer can appear similar, it is recommended to perform ultrasound analyses and possibly tissue sampling with subsequent histopathologic analysis in order to make a proper diagnosis. Unlike typical lumps from breast cancer, fibroadenomas are easy to move, with clearly defined edges.

Fibroadenomas are sometimes called breast mice or a breast mouse owing to their high mobility in the breast.

Fibroadenomas are partially hormone-related and frequently regress after menopause.

Higher intake of fruits and vegetables, higher number of live births, lower use of oral contraceptives and moderate exercise are associated with lower frequency of fibroadenomas.

Paget's disease of the breast is a type of cancer that outwardly may have the appearance of eczema, with skin changes involving the nipple of the breast. The condition is an uncommon disease accounting for 1 to 4.3% of all breast cancers and was first described by Sir James Paget in 1874. The condition in itself often appears innocuous, limited to a surface appearance and it is sometimes dismissed, although actually indicative of underlying breast cancer.

Radial scars are diagnosed by a microscopic examination of excised tissue, i.e. they are diagnosed by pathologists based on their histomorphology.

Ductal carcinoma in situ (DCIS), also known as intraductal carcinoma, is a pre-cancerous or non-invasive cancerous lesion of the breast. DCIS is classified as Stage 0. It rarely produces symptoms or a breast lump one can feel, and is usually detected through screening mammography.

In DCIS, abnormal cells are found in the lining of one or more milk ducts in the breast. "In situ" means "in place" and refers to the fact that the abnormal cells have not moved out of the mammary duct and into any of the surrounding tissues in the breast ("pre-cancerous" refers to the fact that it has not yet become an invasive cancer). In some cases, DCIS may become invasive and spread to other tissues, but there is no way of determining which lesions will remain stable without treatment, and which will go on to become invasive. DCIS encompasses a wide spectrum of diseases ranging from low-grade lesions that are not life-threatening to high-grade (i.e. potentially highly aggressive) lesions.

DCIS has been classified according to the architectural pattern of the cells (solid, cribriform, papillary, and micropapillary), tumor grade (high, intermediate, and low grade), and the presence or absence of comedo histology. DCIS can be detected on mammograms by examining tiny specks of calcium known as microcalcifications. Since suspicious groups of microcalcifications can appear even in the absence of DCIS, a biopsy may be necessary for diagnosis.

About 20–30% of those who do not receive treatment develop breast cancer. It is the most common type of pre-cancer in women. There is some disagreement as to whether, for statistical purposes, it should be counted as a cancer: some include DCIS when calculating breast cancer statistics while others do not.

In breast pathology, a radial scar of the breast, formally radial scar of the breast, is a benign breast lesion that can radiologically mimic malignancy, i.e. cancer.

Radial scar is associated with atypia and/or malignancy and may be an independent risk factor for the development of carcinoma in either breast.

Breast tension is a constellation of symptoms involving the breasts including:

- Breast tenderness

- Breast pain

- Breast engorgement

Breast cancer is cancer that develops from breast tissue. Signs of breast cancer may include a lump in the breast, a change in breast shape, dimpling of the skin, fluid coming from the nipple, or a red scaly patch of skin. In those with distant spread of the disease, there may be bone pain, swollen lymph nodes, shortness of breath, or yellow skin.

Risk factors for developing breast cancer include being female, obesity, lack of physical exercise, drinking alcohol, hormone replacement therapy during menopause, ionizing radiation, early age at first menstruation, having children late or not at all, older age, and family history. About 5–10% of cases are due to genes inherited from a person's parents, including BRCA1 and BRCA2 among others. Breast cancer most commonly develops in cells from the lining of milk ducts and the lobules that supply the ducts with milk. Cancers developing from the ducts are known as ductal carcinomas, while those developing from lobules are known as lobular carcinomas. In addition, there are more than 18 other sub-types of breast cancer. Some cancers, such as ductal carcinoma in situ, develop from pre-invasive lesions. The diagnosis of breast cancer 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 beyond the breast and which treatments it may respond to.

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. A 2009 review for the US Preventive Services Task Force found evidence of benefit in those 40 to 70 years of age, and the organization recommends screening every two years in women 50 to 74 years old. The medications tamoxifen or raloxifene may be used in an effort to prevent breast cancer in those who are at high risk of developing it. Surgical removal of both breasts is another preventative measure in some high risk women. In those who have been diagnosed with cancer, a number of treatments may be used, including surgery, radiation therapy, chemotherapy, hormonal therapy and targeted therapy. Types of surgery vary from breast-conserving surgery to mastectomy. Breast reconstruction may take place at the time of surgery or at a later date. In those in whom the cancer has spread to other parts of the body, treatments are mostly aimed at improving quality of life and comfort.

Outcomes for breast cancer vary depending on the cancer type, extent of disease, and person's age. Survival rates in the developed world are high, with between 80% and 90% of those in England and the United States alive for at least 5 years. In developing countries survival rates are poorer. Worldwide, breast cancer is the leading type of cancer in women, accounting for 25% of all cases. In 2012 it resulted in 1.68 million new cases and 522,000 deaths. It is more common in developed countries and is more than 100 times more common in women than in men.

Comedo mastitis is a very rare form similar to granulomatous mastitis but with tissue necrosis. Because it is so rare it may be sometimes confused with comedo carcinoma of the breast although the conditions appear to be completely unrelated.

Triple-negative breast cancers (TNBC) are sometimes classified into "basal-type" and other cancers; however, there is no standard classification scheme. Basal type cancers are frequently defined by cytokeratin 5/6 and EGFR staining. However, no clear criteria or cutoff values have been standardized yet. About 75% of basal-type breast cancers are triple negative.

Some TNBC overexpress epidermal growth factor receptor (EGFR) or transmembrane glycoprotein NMB (GPNMB).

Upon histologic examination, triple-negative breast tumors mostly fall into the categories of "secretory cell carcinoma" or "adenoid cystic types" (both considered less aggressive); "medullary cancers" and grade 3 invasive "ductal carcinomas" with no specific subtype; and highly aggressive "metastatic cancers". Medullary TNBC in younger women are frequently "BRCA1"-related.

Rare forms of triple-negative breast cancer are "apocrine" and "squamous carcinoma". "Inflammatory breast cancer" is also frequently triple negative.

Many proteins such as Caveolin 1/2, Survivin are researched as possible classification or prognostic factors.

TNBCs have been classified using an integrative analysis of cancer genomics data (DNA copy number, DNA methylation, and mRNA) and PPI data from a prognostic point of view and several key subnetworks (i.e. ubiquitin/proteasome, complement system, metabolism-related Warburg effect, ER-Golgi-cell surface trafficking, transcription) significantly related to patient survival have been identified.