24th May 2025

Breast Lumps

Breast masses are a common clinical finding, particularly in women of reproductive age. Although the vast majority of these masses are benign (over 90%), it is important to exclude breast cancer during the assessment of any patient presenting with a new breast lump.

Fibroadenoma

Fibroadenomas are the most common benign breast tumour, accounting for approximately 50% of all breast biopsies. They can affect women of any age, but are frequently seen in adolescent and young women between the ages of 15 and 35 years. Whilst they typically present as a solitary, unilateral breast lump, in 20% of cases, multiple fibroadenomas may manifest within the same breast or bilaterally.

The aetiology of these lesions remains unknown, however hormonal influences are thought to play a role due to their persistence during reproductive years and typical involution following menopause. Furthermore, changes in their size are often associated with pregnancy or in response to oestrogen therapy.  

Fibroadenomas classically present as a small (1-3cm in size), firm, painless and mobile mass with a smooth texture on clinical examination. Accompanying imaging is usually performed, with ultrasound being the preferred modality in younger women, due to dense breast tissue rendering mammography more challenging. Ultrasound and mammography usually reveal a well-defined, round to ovoid, hypoechoic lesion with smooth margins. Involutional change, typically seen in older, postmenopausal women, may also show characteristic ‘Popcorn calcifications’ on x-ray. 

In cases where there is diagnostic uncertainty, further investigation may be warranted by way of core biopsy or fine needle aspiration (FNA). This may include an enlarging lesion, atypical findings on imaging, a lesion >2.5cm in size or for ‘peace of mind’ for the patient. Histologically, fibroadenomas appear as a biphasic lesion comprising proliferation of both glandular and stromal tissue.

The majority of fibroadenomas do not carry an increased risk of breast cancer and therefore, most patients require no treatment or follow-up. However, surgical excision can be performed if the lesion is particularly large, or at the patient’s request.

Simple Breast Cyst

Breast cysts represent one quarter of all benign breast lesions. As with fibroadenomas, they can affect women of any age, but are more common in women between the ages of 35 and 50 years. The majority of cysts present as a unilateral, solitary mass and are usually found in conjunction with fibrocystic change.

It is believed that most breast cysts result from hormonal influences and their fluctuating levels, resulting in the blockage of the breast acini and a subsequent fluid-filled dilatation of the duct(s). In particular, cysts tend to become larger and painful around menstruation.

A large proportion of women will remain asymptomatic and may be unaware that they have a cyst. In those that do detect a breast lump, cysts typically present as a painful or painless, round to ovoid mass, ranging from a few millimetres to several centimetres in size. Acute enlargement frequently causes severe, localised pain of sudden onset and is usually associated with hormonal changes. However, cysts tend to stop forming in the postmenopausal period and may regress on their own accord.

Clinical examination usually reveals a smooth, firm, discrete, tender mass with a distinct border, said to resemble a ‘grape’ in texture. As with other benign breast disease, accompanying imaging is usually determined by the patient’s age. Features seen on ultrasound include a round to ovoid, anechoic mass, with circumscribed margins and posterior acoustic enhancement. Mammography typically reveals a round to ovoid mass with circumscribed margins only.

Breast cysts are not associated with an increased risk of malignancy and therefore, treatment is not usually indicated. Larger, more painful cysts may be aspirated to provide symptomatic relief. Cytological analysis of the aspirate is only warranted if there are any concerning features, such as blood-stained fluid. Otherwise, the material is typically discarded.

Fat Necrosis

Fat necrosis is a benign breast condition that commonly occurs after direct trauma or surgery to the breast. Whilst it can affect women of any age, middle-aged women seem to be most at risk. Due to its variable character on both examination and imaging, fat necrosis can often mimic malignancy and therefore, may warrant further investigation.

Fat necrosis is characterised by the saponification of fatty tissue, often in response to localised inflammation as a result of direct trauma. The most common causes include breast biopsy, surgery (lumpectomy, reduction, reconstruction, enlargement), lipomodelling and trauma related to seat belts. However, up to 50% of patients may have no history of prior surgery or trauma.

Clinical examination usually reveals a painful or painless, firm, round lump, with a predilection for the subareolar and periareolar regions. The lump may also be associated with changes to the overlying skin, such as erythema, bruising, dimpling or a retracted nipple. Given that the onset can be considerably delayed to the causative event (>10 years), fat necrosis can have a variable appearance on imaging and where possible, comparison with previous imaging is essential.

In the acute phase, ultrasound will show increased echogenicity around the lesion. In the days to months after, the lesion typically develops into an ill-defined complex cystic lesion surrounded by oedematous fat. After several years, fat necrosis may appear as a spiculated mass with calcified walls and posterior shadowing. Mammography, on the other hand, is usually characterised by an ill-defined, irregular, spiculated mass, with or without associated calcification. With time, the lesion will develop into an ‘oil cyst’, characterised by a curvilinear, calcified wall and homogenous centre. 

Due to the potential for diagnostic uncertainty, it may be necessary to biopsy these lesions in order to establish a definitive diagnosis. Histology reveals necrotic fat cells surrounded by macrophages, multi-nucleate giant cells and variable inflammatory cells. More established lesions may show varying degrees of fibrosis and calcifications, as part of a scar formation.

Fat necrosis does not carry an increased risk of breast cancer and therefore, the majority of patients do not require treatment. Surgery is usually avoided, due to the association with developing further fat necrosis. For that reason, intervention is limited to those with symptomatic fat necrosis, persistent/enlarging lesions or for aesthetic purposes.

Phyllodes Tumour

Phyllodes tumours are an uncommon breast neoplasm, accounting for around 1% of all breast tumours. Whilst they can affect women of any age, Phyllodes tumours are more commonly found in premenopausal women between the ages of 40 and 50 years. Akin to a fibroadenoma in their appearance, they are characterised by a fibroepithelial proliferation, with a potential to undergo malignant transformation.

Clinical examination usually reveals a smooth, multinodular, mobile, painless breast mass with rapid growth, averaging 3 to 5cm in size at presentation. Larger tumours can distort the overlying skin, resulting in a shiny, stretched appearance. Palpable axillary lymphadenopathy may also be present in as many as 20% of cases, though the underlying pathology is usually reactive in nature, as opposed to metastatic involvement.

Phyllodes tumours usually appear as a well circumscribed, round-to-oval or lobulated lesion with smooth margins on mammography. A radiolucent halo may also be seen. Ultrasound typically reveals an inhomogeneous, solid appearing mass, largely indistinguishable from a fibroadenoma. As such, imaging alone is insufficient for diagnosis and histological evaluation is necessitated.

Core biopsy is the preferred modality for histological assessment, as fine needle aspiration (FNA) is associated with a high false negative rate and low overall diagnostic accuracy. Histology shows a biphasic proliferation of both epithelial and stromal elements, with an overarching ‘leaf-like’ architecture. Due to the heterogeneity of the tumour, up to 30% of core biopsy specimens may also provide a false negative result and therefore, surgical excision may be required. This may involve breast conserving surgery in the form of a wide-local excision, or a full mastectomy. 

Phyllodes tumours are graded on their histological appearance, which incorporates the degree of cellular atypia, stromal overgrowth and number of mitoses, amongst other features. The vast majority of tumours will fall into the benign category, whilst more atypical tumours may be graded as borderline or malignant. Irrespective of the grading, Phyllodes tumours have a propensity to recur and therefore, follow-up is recommended. However, these tumours are not associated with an increased risk of invasive breast cancer.

Pseudoangiomatous Stromal Hyperplasia (PASH)

Pseuodangiomatous Stromal Hyperplasia (PASH) is a relatively uncommon benign breast condition, that usually affects women of reproductive age. PASH is characterised by a benign proliferation of stromal tissue that mimics a vascular lesion. Typically, it is asymptomatic and therefore, is usually an incidental finding during clinical examination and/or imaging. Whilst hormonal changes are thought to be responsible, the exact aetiology is unknown.

Clinical examination typically reveals a single, painless, well circumscribed mass of varying size, ranging from anywhere between 1cm and 12cm anecdotally. Imaging (both mammography and ultrasound) demonstrates a round, well circumscribed, non-calcified mass, features which are largely non-specific and therefore, histological confirmation is often warranted.

Histology reveals a pattern of slit-like spaces, set within a dense collagenous stroma and lined by spindle shaped myofibroblasts with bland nuclei. The slit-like spaces may resemble vascular channels and as such, PASH may be confused with low grade angiosarcoma.

PASH does not carry an increased risk of breast cancer and for the majority of patients, no treatment or follow-up is indicated. Further assessment is usually reserved for any patients that notice a change in size or character of the lump.