Fibroadenomas are benign proliferations of intralobular stroma. They form circumscribed masses image that bulge out from the adjacent fatty tissue. Clefts image correspond to epithelial-lined spaces.

Fibroadenomas are formed by a proliferation of stromal cells image that usually push and distort the associated epithelium image. These lesions are well circumscribed with pushing borders image.



  • Fibroadenoma (FA)


  • Adenofibroma


  • Biphasic fibroepithelial tumor consisting of intralobular stromal cells and associated epithelial cells


Abnormal Growth of Intralobular Stromal Cells

  • Normal breast development

    • During embryological development, stroma differentiates 1st and induces downgrowth of cells from epidermis to form ductal system

      • This synergistic relationship between epithelial and stromal cells persists in duct/lobular unit

      • Increased growth of stromal cells is accompanied by corresponding hyperplasia of epithelial cells

    • Several possible etiologies for abnormal growth of intralobular stromal cells

  • Hormonal stimulation

    • Most FAs are polyclonal hyperplasias of lobular stroma

      • Some stromal cells have estrogen receptor β &/or progesterone receptors

    • FAs occur most commonly in young premenopausal women

    • FAs can grow during pregnancy

      • If rapid growth occurs, lesion may infarct

      • May be mistaken for malignancy

  • Iatrogenic

    • Cyclosporine in kidney transplant recipients is associated with increase in FAs

      • Attributed to possible similarity to prolactin

      • Can regress when patient is switched to different medication

  • Genetic/hereditary

    • More common in African-American women

    • Myxoid FAs occur in Carney complex

      • Myxomas (cardiac, cutaneous, breast), primary pigmented nodular adrenocortical disease, large cell calcifying Sertoli cell tumors, multiple thyroid lesions, growth hormone-producing pituitary adenoma, other tumors

      • Pigmented skin lesions (lentigos, blue nevi, café au lait spots), typically involving vermillion border of lip and intercanthal portion of eye

      • Type 1 (CNC1): PRKAR1A (17q23-24)

      • Type 2 (CNC2): Locus at 2p16

      • 30% of patients do not have an identified germline mutation

  • Neoplastic

    • Some FAs are monoclonal stromal tumors

      • Clonal genetic changes may be present in stromal cells

      • Associated epithelial cells are usually polyclonal

    • In general, FAs have few genetic changes

      • Some have gain of 1q similar to phyllodes tumors

    • As stromal proliferation becomes more pronounced and autonomous, spectrum of changes seen in FAs overlaps with low-grade phyllodes tumors

      • Some phyllodes tumors likely arise from FAs



  • Incidence

    • Most common solid benign breast lesion

  • Age

    • Typically occur in younger patients (20-35 years)

    • In older women, associated with continued elevated hormone levels either due to replacement therapy or obesity


  • Most commonly presents as painless, slowly growing, mobile, well-defined, palpable nodule in a young woman

  • In older women, may be detected as mammographic circumscribed density or calcifications

Natural History

  • May regress in size with age

  • Stroma typically undergoes hyalinization, which can serve as substrate for calcifications


  • Surgical approaches

    • Most FAs can be diagnosed by core needle biopsy and followed radiographically

    • Surgery to remove a FA may be indicated for large lesions, if patient requests removal, or for rare lesions that continue to grow in size


  • FAs are benign

    • Only clinical importance is in distinguishing FAs from malignancies

    • For some women, FAs may be excised due to cosmetic issues if lesion is large

  • FAs are classified as proliferative breast disease without atypia

    • Relative risk increased 1.5-2x; absolute lifetime risk of breast cancer is 5-7%

    • Risk is to both breasts

    • In 1 study, only women with complex FAs had increased risk

Core Needle Biopsy

  • Diagnosis of FA can usually be made on core biopsy

    • Targeted lesion is usually a circumscribed mass or cluster of calcifications

    • Diagnosis of FA does not correlate well with an irregular mass

  • Some fibroepithelial lesions on core needle biopsy are difficult to classify as FA or phyllodes tumor

    • Stroma may show increased cellularity

    • Mitoses may be present

      • Mitoses > 2 per 10 HPFs favors phyllodes tumor; lower scores do not discriminate between these lesions

      • Ki-67 > 5% favors phyllodes tumor; lower scores do not discriminate between these lesions

      • Because FAs can grow during pregnancy, increased proliferation may be present at this time

    • Focal stromal overgrowth may be seen

    • Infiltration of adjacent stroma may be difficult to evaluate due to fragmentation of cores

  • Certain clinical features increase likelihood that lesion is a phyllodes tumor

    • Large size

    • Increase in size

    • History of prior phyllodes tumor

  • If a definitive diagnosis cannot be made, lesion should be classified as a “fibroepithelial tumor”

    • This type of lesion is best classified after complete surgical excision


Mammographic Findings

  • Circumscribed or lobulated mass

    • May be ill defined if obscured by dense stroma or if fibroadenomatoid changes are present

  • Calcifications may be present, particularly in older women, and will appear as a cluster

    • Calcifications may be coarse (large “popcorn” calcifications) or numerous and small

    • May mimic calcifications seen in DCIS due to clustering

Ultrasonographic Findings

  • Circumscribed or lobulated mass

MR Findings

  • Smooth bordered mass; may have nonenhancing internal septations

  • Enhancement is generally slower than that seen with carcinomas


General Features

  • Circumscribed, white, firm but not hard (rubbery), palpable mass

    • Mass usually bulges above normal breast tissue; slit-like spaces may be present

      • Carcinomas usually do not bulge; typically have flat surface

    • Large FAs may have a leaf-like appearance due to areas of stromal growth separated by epithelial-lined clefts

  • Multiple synchronous FAs can be present


  • Majority < 3 cm but can be very large


Histologic Features

Jul 6, 2016 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on Fibroadenoma

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