Pathology

Breast cancer is more common in the left breast and around 50% arise in the upper outer quadrant. The commonest pathology is ductal carcinoma.

Ductal carcinoma in situ (DCIS)

90% of breast carcinomas arise in the ducts of the breast. They begin as atypical proliferation of ductal epithelium that eventually fill and plug the ducts with neoplastic cells. As long as the tumour remains within the confines of the ductal basement membrane it is classified as DCIS. Localized DCIS is impalpable but often visible on mammography as an area of microcalcification. Not all DCIS will inevitably progress, but the probability of development of invasive cancer is estimated at 30-50%.

Lobular carcinoma in situ

These pre-invasive lesions carry a risk not only of ipsilateral invasive lobular carcinoma but also of contralateral breast cancer. They typically are neither palpable nor contain microcalcification.

Invasive ductal carcinoma

This accounts for 75% of breast cancers. The malignant cells are associated with a fibrous stroma which can be dense (scirrhous carcinoma). The tumour invades through breast tissue into the lymphatics and vascular spaces, to gain access to the regional nodes (axillary and, less often, internal mammary) and the systemic circulation.

Table 17.2 Histological types of breast malignancy

♦ Invasive ductal carcinoma

No special type Combined with other type Medullary carcinoma Mucinous carcinoma Paget's disease

♦ Invasive lobular carcinoma

♦ Mixed lobular and ductal carcinoma

♦ Metastases (e.g.breast cancer,small cell lung cancer)

The histological grade of the tumour is assessed from three features (tubule formation, nuclear pleomorphism, and mitotic frequency) and predicts the behaviour of the tumour. Oestrogen and progesterone receptor status is commonly assessed by immunocyto-chemistry. Other biological markers (e.g. c-erbB2) may be of value both as a predictor of prognosis and as a guide to therapy.

Ductal carcinoma of special type

A number of pathological variants are identified with relatively good prognosis, namely medullary carcinoma, tubular carcinoma, and mucinous carcinoma. Paget's disease of the breast is ductal carcinoma of the excretory ducts with involvement of the skin of the nipple and areola.

Invasive lobular carcinoma

Lobular carcinomas account for 5-10% of breast cancers. About 20% develop contralateral breast cancer.

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