RESUMO
PURPOSE: To develop a simple and practical formula for quantifying breast cancer-related lymphedema, accounting for both the asymmetry of upper extremities' volumes and their temporal changes. METHODS AND MATERIALS: We analyzed bilateral perometer measurements of the upper extremity in a series of 677 women who prospectively underwent lymphedema screening during treatment for unilateral breast cancer at Massachusetts General Hospital between August 2005 and November 2008. Four sources of variation were analyzed: between repeated measurements on the same arm at the same session; between both arms at baseline (preoperative) visit; in follow-up measurements; and between patients. Effects of hand dominance, time since diagnosis and surgery, age, weight, and body mass index were also analyzed. RESULTS: The statistical distribution of variation of measurements suggests that the ratio of volume ratios is most appropriate for quantification of both asymmetry and temporal changes. Therefore, we present the formula for relative volume change (RVC): RVC = (A(2)U(1))/(U(2)A(1)) - 1, where A(1), A(2) are arm volumes on the side of the treated breast at two different time points, and U(1), U(2) are volumes on the contralateral side. Relative volume change is not significantly associated with hand dominance, age, or time since diagnosis. Baseline weight correlates (p = 0.0074) with higher RVC; however, baseline body mass index or weight changes over time do not. CONCLUSIONS: We propose the use of the RVC formula to assess the presence and course of breast cancer-related lymphedema in clinical practice and research.