Non-breast cancer mortality after conservative surgery and radiation therapy (RT) to the left breast

Purpose: Post-operative RT to the left chest wall using older techniques is associated with an increased risk of cardiac mortality that begins to be apparent at 10 years. A critical question remains whether left-breast RT as part of breast-conserving therapy leads to a similar increase using modern megavoltage techniques. To address this, we attempted to determine whether patients treated with left-breast RT using modern techniques have a higher long-term risk of non-breast cancer mortality than patients treated with RT to the right breast. Materials and Methods: Between 1968-86, 1624 pts were treated for clinical Stage I or II invasive breast cancer with gross excision and ≥60 Gy to the tumor bed. Fifteen pts (<1%) were treated with a separate RT field to the internal mammary nodes and were excluded from further analysis. Of the remainder, 53 pts (3%) have been lost to follow-up for ≥3yrs (after 6-181 months). Median follow-up for 1076 survivors is 137 months (6-278). Pts were divided into two groups: 825 pts (51%) received RT to the left breast and 784 pts (49%) received RT to the right breast. Clinical, pathologic, and treatment data were compared between the two groups. Twelve-year crude mortality rates from breast cancer and from other causes were calculated for each pt group among 833 pts with potential follow-up of at least 12 years (Table 1). Yearly hazard rates for non-breast cancer mortality were also calculated for each pt group (Figure 1). Results: The pts treated with left RT and right RT were well-balanced with regards to most clinical, pathologic, and treatment variables. Median age at diagnosis was 51 and 52, respectively, for pts with left RT and right RT (p=NS). A statistically significant difference was noted in the incidence of nodal positivity between the two groups (33% left vs. 38% right, p=0.03) although the median number of positive nodes, in pts with any positive nodes, was identical (2) in the two groups. Conclusions: Patients in this series who received left-breast RT using modern megavoltage techniques do not have a higher risk of non-breast cancer mortality than pts who were treated with right-breast RT. These data suggest that any effect of modern, left-breast RT on cardiac mortality is likely to be minimal. Further follow-up (particularly detailing causes of non-breast cancer mortality) is required on patients treated with modern techniques