Acute mastitis is the most common inflammatory disorder of the breast, and is usually confined to the lactation period. During breastfeeding, the nipple can develop fissures and cracks. Via these cracks, bacteria (usually Staphylococcus aureus) gain access to the breast tissue. The infection is usually confined to one segment of the breast, and is manifest by oedema and erythema of the overlying skin.

If severe and untreated, the acute inflammation may progress to abscess formation.

This term is used to refer to dilatation of the breast ducts. The ducts become filled with inspissated breast secretions and there is associated inflammation and fibrosis. If there is an unusually heavy infiltrate of plasma cells, the term ‘plasma cell mastitis’ is sometimes applied. The aetiology of mammary duct ectasia is unknown. Affected women can present with a palpable mass, skin retraction or nipple discharge, which can occasionally be blood-stained. The lesion is of clinical importance because it can be mistaken for carcinoma clinically, grossly and mammographically.

This lesion is usually related to previous trauma to the breast, although a history of trauma may not always be obtained. Histologically, there is an initial focus of necrotic fat cells and acute inflammation, which then becomes heavily infiltrated by macrophages that engulf the debris and hence develop a lipid-laden ‘foamy’ appearance. With healing, the focus often becomes replaced by fibrous tissue and there may be (dystrophic) calcification. Affected women present with a palpable breast lump or nipple retraction, raising the suspicion of carcinoma. If there is calcium deposition, lesions may also mimic carcinoma mammographically.

This condition is rare. Causes include infections (e.g. tuberculosis, deep-seated fungal infections) and systemic disorders (e.g. Wegener’s granulomatosis, sarcoid).

This term denotes an increase in the number of acini within a lobule. The gland lumina in adenosis occasionally contain calcium deposits.

This term refers to cystic dilatation of acini or terminal ducts. Some cysts may reach a very large size (up to 2–3cm across). The secretions within cysts may calcify.

This is probably a secondary event to rupture of cysts and it may proceed to hyalinisation.

In this condition, there is an increased number of acini and increased intralobular fibrosis. The fibrosis causes marked distortion of the acini. The lesion can present as a mammographic density or a palpable mass, therefore mimicking carcinoma. Sclerosing adenosis may be mistaken for carcinoma histologically also. Radial scars and complex sclerosing lesions are morphological variants of sclerosing adenosis, and are characterised by:

Radial scar is the term reserved for lesions less than 10mm in diameter, whereas larger lesions are called complex sclerosing lesions. They can mimic carcinoma clinically, mammographically and histologically.

Epithelial hyperplasia is defined as an increase in the number of layers of cells lining the acini or ducts, often resulting in the obliteration of their lumen. Epithelial hyperplasia is classified as being either of usual type or atypical.

Fibroadenomas are the most common benign tumour of the breast. The tumours are composed of both glandular and stromal tissue. These benign neoplasms can occur at any age, but they are most commonly seen in women under 35years of age. Fibroadenomas are usually solitary, although in some women they may be multiple and bilateral. In younger women they present as palpable lumps (often freely mobile), and in older women they may present as mammographic densities. They can therefore mimic carcinoma clinically.

Fibroadenomas grow within the breast as sharply circumscribed soft to firm nodules, and are usually easily enucleated at surgery. They vary in size from less than 1cm to around 4cm in diameter, although rarely they can reach up to 15cm in diameter (juvenile fibroadenoma/giant fibroadenoma – see below). The cut surface is grey-white and sometimes glistening, and contains slit-like spaces. In older women, fibroadenomas can become calcified. Histologically, these tumours are well-circumscribed nodules consisting of loose cellular stroma associated with breast ducts that, in longitudinal section, appear as compressed and elongated clefts.

The vast majority of fibroadenomas are benign. However, those containing cysts, sclerosing adenosis, epithelial calcification or papillary apocrine change (so-called complex fibroadenomas) are associated with an increased risk of developing breast cancer.

Duct papillomas are uncommon and are usually seen in middle-aged women. They appear as outgrowths projecting into the duct lumen and consist of a fibrovascular core covered by benign breast duct epithelium. There are two types of duct papilloma:

Adenomas of the breast are rare. There are three main subtypes:

It has long been known that there is a familial aggregation of breast cancer, and at least four genes that convey increasing susceptibility to breast cancer have been identified. These are:

Genetic predisposition is responsible for only 5–10% of breast cancer cases.

Breast cancer is uncommon before the age of 25years, but the incidence increases steeply with age, doubling about every 10years until the menopause. The rise slows in the postmenopausal period.

Early age at menarche and late age at menopause are associated with an increased risk of breast cancer. These findings indicate that hormones may have an important role in the development of carcinoma of the breast.

An early age at first pregnancy is associated with a decreased risk of developing breast cancer.

The incidence of breast cancer in Western countries is around five times higher than that in Far Eastern countries. Also, the rate of breast cancer is higher in women of high socioeconomic status. These differences are thought to be related to differing reproductive patterns, such as age at first birth, age at menarche and age at menopause.

Exposure to ionising radiation increases the risk of breast cancer. The greatest risk has been found among women exposed to radiation around the menarche.

The risk of breast cancer varies according to the type of benign breast disease (see above).

Women with breast cancer have an increased risk of developing a new primary lesion in the contralateral breast or the conserved ipsilateral breast.

The role of obesity, diet and alcohol as risk factors for the development of breast cancer remains controversial and unresolved.

This term is used to refer to the situation where the malignant cells are confined to the ducts or acini, with no evidence of invasion by the tumour cells through the basement membrane and into the breast stroma. Women with these lesions have a markedly increased risk (8–10 times) of developing breast cancer. There are two types of non-invasive carcinoma:

In this type of non-invasive carcinoma, the malignant cells are found in the acini, although the changes seen may extend into the ducts. LCIS is often multifocal within one breast and frequently bilateral. The lesions do not present as palpable lumps and calcifications rarely occur, which means that they are rarely detected by mammography. Hence, the lesions are usually identified incidentally in biopsies for other breast abnormalities.

With invasive carcinoma, the malignant cells have breached the basement membrane of the ducts or acini, and have spread into the surrounding stromal tissue.

This condition presents as roughening and reddening of the skin of the nipple and areola, the appearances resembling eczema. Ulceration may occur. The condition is important to recognise because it is associated with underlying in situ or invasive carcinoma of the breast. Histologically, the epidermis is infiltrated by malignant cells.

Breast carcinomas spread locally in all directions, becoming adherent to the underlying muscle fascia of the breast or tethered to the overlying skin. The latter manifests by dimpling of the skin and nipple retraction.

Involvement of the breast lymphatics by carcinoma causes blockage of the lymphatic drainage with consequent lymphoedema and thickening of the overlying skin, an appearance referred to clinically as peau d’orange. Several groups of lymph nodes drain lymph from the breast, but the axillary lymph nodes are the commonest initial site of lymph node metastases. Around a third of women with breast cancer will have lymph node metastases at the time of diagnosis.

Once the malignant cells have developed the ability to enter the bloodstream, they can reach virtually any organ in the body, but the most frequently affected sites are the lungs, bones, liver, adrenals and brain.

Two main systems are used to stage breast cancer. These are the International Classification of Staging of Breast Cancer, and the TNM (tumour, node, metastasis) system. The management of the patient will depend on the stage of the disease (Table 36).

Small tumours are associated with a more favourable prognosis.

Many studies have shown the value of histological grade in predicting survival in breast cancer, low-grade cancers being associated with a more favourable prognosis.

Certain types of breast carcinoma have a better prognosis than others, although the significance is less important than histological grade. Tubular carcinoma (and probably mucinous, medullary and papillary carcinoma) have a more favourable prognosis than invasive ductal carcinoma of no special type.

Women with oestrogen receptor-positive (ER+ve), node-negative breast cancer have a better prognosis than those who have oestrogen receptor-negative (ER−ve) tumours. This is probably because tumours that express oestrogen receptors respond well to hormonal manipulation. The progesterone receptor status of a tumour is less important than the oestrogen receptor status, but it may have a small effect on the overall responsiveness of a tumour to hormonal manipulation in that women with ER+ve tumours which are also progesterone receptor positive (PR+ve) have a slightly increased chance of benefiting while those with tumours that are ER+ve and PR−ve have a slightly decreased chance of benefiting. Tumours that are both ER−ve and PR−ve are less likely to respond to hormonal manipulation than tumours which are ER−ve and PR+ve.

It has been proposed that tumour differentiation, invasion, metastasis, and growth can be inferred by measuring certain cellular markers, e.g. expression of growth factor receptors, proteinases, cell-adhesion molecules, and other products of oncogenes and tumour suppressor genes. Much of the research in this field has focused on the oncogene HER2 (also known a HER2/NEU and c-ERB-B2), the protein product of which is a cell-surface growth factor receptor. Research using molecular techniques indicates that 1 in 4 breast carcinomas show amplification of the HER2 gene and such cancers are referred to as ‘HER2-positive’. Studies have shown that HER2-positive cancers have a poorer prognosis, shorter survival, shorter relapse time, tend to be more aggressive and respond poorly to conventional therapies. However, it has now been possible to develop a treatment strategy that employs the use of a monoclonal antibody called trastuzumab (Herceptin), which can block the HER2 receptor and hence reduce tumour growth. Evidence indicates that administration of this antibody to women with HER2-positive breast cancers may significantly improve survival.

Like fibroadenomas, phyllodes tumours are composed of both glandular and stromal tissue, are usually solitary, and can present as palpable lumps or mammographic densities. They can occur at any age but the median age at presentation is 45years, some 10–20years later than that for fibroadenomas. Phyllodes tumours can only be differentiated from fibroadenomas by their microscopic appearance.

Sarcomas such as angiosarcoma, fibrosarcoma, liposarcoma and leiomyosarcoma are all rare.

Lymphomas in the breast may be primary, but are more usually secondary to disease elsewhere in the body.

Secondary tumours to the breast are rare. Those most commonly encountered are metastases from the lung, the contralateral breast and malignant melanoma.

Gynaecomastia is thought to occur as a result of an imbalance between oestrogens (which stimulate the breast) and androgens. The condition can occur as a normal phenomenon in adolescents and very elderly men, but it can also occur in the following situations: