Interlobular stromal lesions and other breast malignancies

Lesion

The fatty and fibrous tissue between lobules makes the same tumours as soft tissue elsewhere; the important malignant ones are angiosarcoma and lymphoma.

Updated Nov 12, 2026

Key points

PASH: slit-like spaces lined by myofibroblasts that mimic vascular channels; hormone-driven; benign but must not be confused with angiosarcoma.
Fibromatosis: infiltrative bland spindle cells; CTNNB1 or APC mutations, nuclear beta-catenin; locally aggressive, no metastasis.
Myofibroblastoma: well-circumscribed spindle-cell tumour, common in men; 13q loss.
Angiosarcoma: primary in younger women, or secondary in irradiated skin years after breast-conserving treatment (MYC amplification), or in a lymphoedematous arm after mastectomy (Stewart–Treves).
Lymphoma: diffuse large B-cell lymphoma is the most frequent primary breast lymphoma; breast implant–associated anaplastic large cell lymphoma (CD30-positive, ALK-negative) forms in the seroma around textured implants.
Metastases to the breast: melanoma, lung, ovary and the opposite breast.

What it is

The interlobular stroma is ordinary fibrous and fatty connective tissue, so it gives rise to the same tumours as soft tissue elsewhere. Benign lesions include pseudoangiomatous stromal hyperplasia, myofibroblastoma, fibromatosis (desmoid tumour), lipoma, haemangioma and granular cell tumour. The most important sarcoma is angiosarcoma, which arises spontaneously in younger women or after radiation therapy and lymphoedema. Other malignancies of the breast include lymphoma, among them the lymphoma that forms around textured implants, and metastases from other organs.

Structure

Angiosarcoma: haemorrhagic, ill-defined mass or purple skin lesions; anastomosing vascular channels dissecting fat and stroma, lined by atypical endothelial cells (CD31, ERG).
Fibromatosis: long fascicles of uniform myofibroblasts infiltrating fat and muscle at the edges.
Implant-associated lymphoma: large atypical CD30-positive cells in the fluid or the capsule around the implant.

Step by step

Stromal fibroblasts, myofibroblasts, fat and vessels between lobules can each give rise to a tumour.
Radiation damages endothelial cells of the treated skin and breast, and years later an angiosarcoma may arise.
Chronic lymphoedema impairs local immunity and drives lymphatic proliferation, favouring Stewart–Treves angiosarcoma.
Chronic inflammation around textured implants can select a T-cell clone that becomes anaplastic large cell lymphoma.

Markers

CD31, ERG and MYC (angiosarcoma)
Nuclear beta-catenin (fibromatosis)
CD30 with ALK negative (implant lymphoma)
CD34 and PR (PASH)

Clinical notes

New bruise-like skin discoloration or nodules in a previously irradiated breast should be biopsied to exclude angiosarcoma.
A late seroma around a breast implant is aspirated and tested for implant-associated lymphoma.
A breast mass in a patient with known melanoma or lung cancer may be a metastasis rather than a new primary.

Test yourself

Think of the answer, then tap the question to see it.

What is Stewart–Treves syndrome?

Angiosarcoma arising in a chronically lymphoedematous arm after mastectomy with axillary node dissection.

Which lymphoma is associated with textured breast implants?

Breast implant–associated anaplastic large cell lymphoma, CD30-positive and ALK-negative.

Why must PASH be distinguished from angiosarcoma?

Its slit-like stromal spaces mimic vascular channels, but they are lined by benign myofibroblasts, not atypical endothelial cells.

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Elsewhere in DurgiPedia

Breast: ducts, lobules and changes with life stage

Connections

← All of general pathology

Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.

Sources: Breast Cancer Treatment (PDQ®)–Health Professional Version (National Cancer Institute, 2026).

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Representative model, for educational purposes only.