Fibroadenomas are the most common benign breast tumor in women under 35 years of age. Hormonal factors are thought to contribute to fibroadenoma growth, but the exact etiology is poorly understood. On examination, fibroadenomas are well-defined, mobile, typically solitary breast masses that are 1–2 cm in diameter on average. Giant fibroadenomas are much larger in size and can distort the shape of the breast. Patient history, physical examination, and are used to establish the diagnosis. Biopsy is not routinely required for diagnostic confirmation but may be indicated to rule out differential diagnoses (e.g., phyllodes tumor, breast cancer). Although most fibroadenomas are benign and have an excellent prognosis, complex adenomas are associated with an increased risk of breast cancer.
- Usually a well-defined, mobile mass
- Most commonly solitary
- Rubbery consistency
- Typically 1–2 cm in diameter
- Giant fibroadenomas are > 5 cm in size and may distort the shape of the breast. 
Follow age-appropriate diagnostic workup for a. The findings specific to fibroadenoma are described here.
- Breast ultrasound: well-circumscribed oval or round hypoechoic solid mass with no posterior acoustic shadowing 
- Round mass with a well-defined border
- May have popcorn-like calcifications
- Breast MRI : The appearance varies depending on whether hyalinization is present.
- Indications (not routinely indicated): imaging or clinical findings suspicious for malignancy or phyllodes tumor 
- Modalities: , fine needle aspiration, or excisional biopsy 
- Findings: fibrous and glandular tissue 
- Tend to be larger in size
- Often grow more rapidly than fibroadenomas
- Usually occur in women ∼ 40 years of age
- Other breast cysts) (e.g.,
- Breast cancer
The clinical and imaging features of phyllodes tumors may closely resemble those of fibroadenomas, but the biological behaviors of these tumors are different. Borderline and malignant phyllodes tumors can metastasize hematogenously, and benign phyllodes tumors have a high risk of recurrence postexcision.
The differential diagnoses listed here are not exhaustive.
Management decisions should be made using shared decision-making.
- Fibroadenomas < 2 cm in size 
- Asymptomatic adolescent patients 
Measures: routine clinical breast exams (CBE) and
- Lesions diagnosed as fibroadenoma on imaging alone: Short-term (every 6 months for 2 years) follow-up with imaging is recommended. 
- Biopsy-proven fibroadenomas: Longer surveillance intervals may be considered. 
- Large size (e.g., > 2 cm) or rapid growth
- Suspected malignancy
- Bothersome symptoms or cosmetic concerns