Breast fibroadenoma histology

Macroscopic appearance and secondary changes

Clinically, fibroadenoma presents as a dense, completely painless, solitary node with clear margins. Despite the absence of a true connective tissue capsule, surgeons note an important feature: during surgery, the node easily "shells out" from the surrounding healthy breast tissue.

On cross-section, the gross specimen appears as a homogenous grayish-white tissue. Over time, secondary changes may develop within the tumor, including:

• Foci of hyalinosis.
• Areas of myxoid change.
• Calcifications (calcium salt deposits).

There are also rare clinical forms of the pathology, such as multiple fibroadenoma, in which individual nodes can reach giant sizes (up to 20 cm in diameter).

Histological variants

The microscopic appearance of a fibroadenoma always consists of two structures: fibrous stroma and epithelial ducts. Depending on how the connective tissue interacts with the glandular elements, two histological variants are distinguished:

1. Intracanalicular: actively proliferating stroma compresses the glandular structures. As a result of this mass effect at the micro-level, the ducts are deformed and take the form of narrow slits or branching bands.
2. Pericanalicular: fibrous stroma proliferates in concentric circles, surrounding the ducts from the outside. In this case, the glandular spaces are not compressed and retain a regular round or oval shape.

Regardless of the identified type, the prognosis for the patient is equally favorable. Provided complete surgical excision is performed, the tumor typically does not recur.

Radiological appearance and microcalcifications

On mammograms, fibroadenomas often undergo calcification, which is especially characteristic of postmenopausal patients. A classic radiological sign in this case is the "popcorn" sign — the visualization of large and coarse calcifications.

However, if the salt deposits appear as small and punctate (punctate), standard radiological imaging becomes insufficient. To establish an accurate diagnosis and rule out ductal carcinoma in situ (DCIS), a percutaneous biopsy is mandatory.

It is important to remember that some malignant tumors can mimic benign nodes. For example, rapidly growing aggressive triple-negative cancers (ER-, PR-, HER-2-) sometimes have relatively clear margins, visually mimicking a fibroadenoma on images.

Differential diagnosis

During histological and radiological examination, fibroadenoma must be differentiated from other breast processes:

• Phyllodes tumor: like fibroadenoma, it consists of epithelium and mesenchyme. Its main difference is that the stroma has increased cellularity and forms specific leaf-like structures on cross-section. In addition, it is rare (0.3–1% of primary tumors) and is diagnosed in older women — at 40–50 years.
• Fibroadenomatous hyperplasia: histologically combines microscopic features of fibroadenoma and fibrocystic mastopathy. Unlike a true tumor, it usually does not cause a mass effect on tissues, but often requires biopsy to rule out malignancy.
• Lipoma: a well-circumscribed fat-density lesion with a thin capsule. On ultrasound, unlike fibroadenoma, it appears as a hyperechoic mass.

Class and exam questions

What else to study on this topic

• Histogenesis and morphological features of the phyllodes tumor
• Microcalcifications: differential diagnosis on mammography ("teacup", "eggshell" signs)
• Radial scar: microscopic appearance and association with epithelial atypia
• Triple-negative breast cancer: aggressiveness and radiological characteristics
• Histological grade of tumor malignancy (role of tubule formation and nuclear pleomorphism)

Other topics in the "Additional Topics" section

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.