Fibroadenoma is a type of benign breast tumour and is the most common cause of breast mass, frequently seen in women of reproductive age. The incidence of fibroadenoma in women is reported as between 7% to 13%. Fibroadenomas are sometimes colloquially referred to as breast mice. This condition is most frequently managed conservatively, with reassurance, as it does not progress to breast cancer and frequently may shrink over time.

Fibroadenoma is most common in young women of reproductive age and its incidence in men is rare.

Fibroadenoma is most common

• During menses
• During pregnancy
• Whilst using combined oral contraceptives.

The exact aetiology is unknown but there is belief that given this distribution, it is related to the sensitivity of breast tissue to oestrogen.

There is also believed to be a genetic component including MED12 (mediator complex subunit 12) gene related to fibroadenoma.

Fibroadenomas are benign and do not mutate into malignancy. Though they represent a proliferation of breast tissue, fibroadenomas do not exhibit any pleomorphism.

Fibroadenomas arise from the terminal duct lobular unit. They are comprised of both stromal tissue and epithelial connective tissue cells. As they contains two different cellular types, they are considered biphasic. On histological assessment, they appear as sheets of epithelial cells in a honeycomb or antler-like pattern.

The stromal and epithelial cells can be arranged in two patterns:

• Pericanalicular: stromal cells proliferate surrounding epithelial structures
• Intracanaliccular: stromal cells proliferate invaginating the glandular tissue

It is possible that a patient with fibroadenoma may experience no symptoms and be fully asymptomatic, including not recognising presence of the fibroadenoma.

In patients who are symptomatic, the fibroadenoma mass is:

• Painless / non-tender
• Mobile / non-tethered
• Smooth
• Well-circumscribed
• Solitary
• 2-3 cm in diameter (except for giant fibroadenoma, which comprises 1% of breast masses and can measure up to 5cm)

Fibroadenomas are most often found within the upper outer quadrant of the breast. There are not usually any overlying skin changes.

As per NICE recommendations, an urgent 2-week-wait suspected cancer referral should be made for patients aged 30 and over who have an unexplained breast lump with or without pain. A non-urgent referral should be considered in patients under 30 with an unexplained breast lump with or without pain.

Often trusts have a 'one-stop' clinic where clinical examination, imaging and pathology investigations are offered. Based on these, a patient will have a risk assessment including an examination score graded from P1 (normal) - P5 (malignant), as well as imaging scores from M1-M5 or U1-U5, depending on modality, and pathology scores from B1-B5.

Where imaging is recommended:

• Ultrasound is used predominantly in younger women, under age 35 and in men, as it has greater sensitivity in denser breast tissue.
• Mammograms are preferred in women 35 and over.
• MRI is not routinely used.

Histology can be offered in the form of core biopsy, which allows for a full histopathological assessment, or a fine-needle-aspiration-cytology (FNAC), in which only cytology can be offered.

Possible differential diagnoses:

• Fibrocystic changes
  • Similarities: smooth lumpy changes in the breast, most prominent in reproductive years, related to menses
  • Differences: usually presents with multiple bilateral lumps
• Infection (e.g. mastitis)
  • Similarities: localised breast swelling, most often unilateral
  • Differences: associated with redness, warmth, pain and systemic symptoms including fever
• Breast cancer
  • Similarities: unilateral breast mass
  • Differences: can have overlying skin changes, including affecting nipple. Can be associated with discharge and pain. If progressive, can have associated systemic/constitutional symptoms
• Breast cyst
  • Similarities: distinct, mobile round or oval masses, with onset that can be related to menses
  • Differences: age of onset of breast cyst is older, at 35-50 years old. May present with nipple discharge and pain/tenderness
• Phyllodes tumor
  • Similarities: also presents as smooth, firm, well circumscribed mass
  • Differences: age of onset of phyllodes tumour is older, at 40-50 years old. Phyllodes tumours are faster growing.

According to NICE recommendations, an asymptomatic fibroadenoma does not require treatment or follow-up. However, NICE recommends that growth in fibroadenoma size or other changes should warrant repeat investigation. NICE recommends symptomatic fibroadenomas can be removed if troublesome.

Options for removal include:

• Surgical lumpectomy or excisional biopsy may be used to remove the mass (the mass can then undergo additional histopathological analysis)
• Vacuum-assisted biopsy
• Cryoablation, in which the application of low temperatures is used to destroy breast tissue (this is offered after histological/cytological confirmation)
• High intensity focussed ultrasound for ablation of fibroadenoma tissue (still in preliminary use, as suggested by NICE)

Indications for surgical removal may include large size, continued growth of mass or patient request. There is no consensus guidance on surgical treatment of fibroadenoma, though giant fibroadenomas (mass greater than 500 g or size larger than 5 cm) are generally removed.