Relationship between tumor location and relapse in 6,781 women with early invasive breast cancer.

PURPOSE: To explore the independent prognostic impact of medial hemisphere tumor location in early breast cancer. PATIENTS AND METHODS: A comprehensive database was used to review patients referred to the British Columbia Cancer Agency from 1989 to 1995 with early breast cancer. Patients were grouped according to relapse risk (high or nonhigh) and adjuvant systemic therapy received. Multiple regression analysis was used to determine whether the significance of primary tumor location (medial v lateral hemisphere) was independent of known prognostic factors and treatment.
RESULTS: In the adjuvant systemic therapy groups, medial location was associated with a 50% excess risk of systemic relapse and breast cancer death compared with lateral location. Five-year systemic disease-free survival rates were 66.3% and 74.2% for high-risk medial and lateral lesions, respectively (P <.005). Corresponding 5-year disease-specific survival rates were 75.7% and 80.8%, respectively (P <.03). No significant differences were observed between medial and lateral location for low-risk disease regardless of adjuvant therapy or for high-risk disease with no adjuvant therapy. Local recurrence rates were similar for all risk and therapy groups.
CONCLUSION: The two-fold risk of relapse and breast cancer death associated with high-risk medial breast tumors may be due to occult spread to internal mammary nodes (IMNs). Enhanced local control, such as with irradiation of the IMN chain, may be one way to reduce the excess risk. Ongoing randomized controlled trials may provide prospective answers to the question of the optimal volume of radiotherapy.