3-DIMENSIONAL STAGING OF BREAST-CANCER

Purpose: Breast cancers are three dimensional solids but very few are spherical. We hypothesized that calculations based on the greatest dia meter would not accurately reflect tumor volume and that three dimensi onal measurements would affect tumor staging. Materials and methods: 1 65 invasive carcinomas measuring 2.5 cm or less and having three measu red diameters (a greater than or equal to b greater than or equal to c ) noted were evaluated. Tumor volume was calculated using four geometr ic models: the spherical 4/3 pi (a/2)(3), prolate spheroid 4/3 pi (a/2 ) (c/2)(2), oblate spheroid 4/3 pi (a/2)(2) (b/2), and ellipsoid 4/3 p i (a/2 x b/2 x c/2. The ellipsoid correctly determined the volume for any tumor shape. All cases were stratified according to the TNM stagin g system. Differences in mean volume calculated as a sphere and ellips oid for each tumor subclass were analyzed using Student's T test. The reclassification of tumors by the ellipsoid formula was determined. Re sults: Seventy-six (46.1%) had tumors with three different diameters w hile only six (3.6%) were true spheres having three identical diameter s, Mean tumor volume analysis of T-1a, T-1b, T-1c, and T-2 tumors demo nstrated a statistically significant overestimation of volume when uti lizing the sphere formula instead of the ellipsoid formula (p < 0.05). The differences in volume were more dramatic as the diameters increas ed. A total of 41 tumors were moved into smaller T subclasses includin g 10 node positive patients. Conclusions: Tumor volume analysis demons trates that use of only the greatest diameter poorly reflects the true volume of a lesion and consistently overestimates volume. The ellipso id formula accurately calculates volume for these three dimensional tu mors and when utilized has significant relevance to staging small inva sive breast cancers.