[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [General pathology](https://durgical.com/en/general-pathology/) › [Breast](https://durgical.com/en/general-pathology/areas/breast/) › Interlobular stromal lesions and other breast malignancies # 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. ## Memory aid Between the lobules lives ordinary connective tissue: it makes ordinary soft-tissue tumours, but angiosarcoma after radiation is the one not to miss. ## 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. [Add to my cards (3)](https://durgical.app/estudiar/?add=/en/general-pathology/interlobular-stromal-lesions-and-other-breast-malignancies/) [More Pathology questions →](https://durgical.com/en/practice/?f=pathology) ## Elsewhere in DurgiPedia - [Breast: ducts, lobules and changes with life stage](https://durgical.com/en/histology/breast-ducts-lobules-and-changes-with-life-stage/) ## Connections ## Related 7 - [Tumours of the intralobular stroma: fibroadenoma vs phyllodes tumour](https://durgical.com/en/general-pathology/tumours-of-the-intralobular-stroma-fibroadenoma-vs-phyllodes-tumour/) - [Haemangioendothelioma and angiosarcoma](https://durgical.com/en/general-pathology/haemangioendothelioma-and-angiosarcoma/) - [Benign vascular tumours](https://durgical.com/en/general-pathology/benign-vascular-tumours/) - [Nodal T-cell lymphomas](https://durgical.com/en/general-pathology/nodal-t-cell-lymphomas/) - [Diffuse large B-cell lymphoma](https://durgical.com/en/general-pathology/diffuse-large-b-cell-lymphoma/) - [Radiation and cancer: ultraviolet and ionizing](https://durgical.com/en/general-pathology/radiation-and-cancer-ultraviolet-and-ionizing/) - [Benign vs malignant tumours: the comparison table](https://durgical.com/en/general-pathology/benign-vs-malignant-tumours-the-comparison-table/) ## Related conditions 5 - [Soft tissue sarcomas (liposarcoma, leiomyosarcoma, rhabdomyosarcoma)](https://durgical.com/en/conditions/soft-tissue-sarcomas/) - [Non-Hodgkin lymphoma](https://durgical.com/en/conditions/non-hodgkin-lymphoma/) - [Breast cancer](https://durgical.com/en/conditions/breast-cancer/) - [Melanoma](https://durgical.com/en/conditions/melanoma/) - [Lung cancer](https://durgical.com/en/conditions/lung-cancer/) [← All of general pathology](https://durgical.com/en/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](https://www.cancer.gov/types/breast/hp/breast-treatment-pdq) (National Cancer Institute, 2026). ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/general-pathology/interlobular-stromal-lesions-and-other-breast-malignancies/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/general-pathology/interlobular-stromal-lesions-and-other-breast-malignancies/