39 - Breast Metastasis

Summary

PATTERNS OF METASTATIC SPREAD

Background

Breast cancer is an important public health problem, with more than one million new cases worldwide annually. In the developed world, early-stage disease represents an increasing proportion of incident breast cancer diagnoses, whereas metastatic breast cancer (MBC) without a preceding diagnosis of early-stage disease is a rare event. However, despite an early-stage diagnosis, up to one-third of patients will experience distant relapse. MBC is treatable but incurable, with a median survival of two to three years. Consequently, clinicians often recommend systemic adjuvant therapy for patients with early breast cancer (EBC), as it prevents or delays the development of incurable metastatic disease. Adjuvant therapy may comprise hormonal therapy, cytotoxic chemotherapy, and targeted therapy, depending on the breast cancer subtype, the individual's risk of recurrence, and various patient-specific factors including age, menopausal status, and comorbid conditions.

Breast cancer is a heterogenous disease with respect to natural history and response to therapy. More than 95 percent of breast cancers arise from the breast epithelium and are carcinomas. The two most common histological subtypes are invasive ductal carcinoma (IDC) and invasive lobular carcinoma (ILC), which account for approximately 75 percent and 15 percent of breast cancers, respectively. IDC cells are typically clustered in well-formed glandular structures, whereas ILC cells are frequently organized in single file. These distinct cellular patterns are commonly used to distinguish the two histologic subtypes.