Comparative analysis of size estimation by mapping and counting number of blocks with ductal carcinoma in situ in breast excision specimens.

CONTEXT: The size of ductal carcinoma in situ (DCIS) is a significant predictor of local tumor recurrence and is used for selection of patients for conservative versus aggressive therapy. A standardized method for size assessment is lacking. OBJECTIVE: To evaluate 2 commonly used methods for measurement of DCIS extent: one based on the distribution of the lesion in sequential series of sections (mapping method) and the other on the number of sections with DCIS (block method). DESIGN: Ninety-eight consecutive cases of DCIS, measuring at least 1.0 cm, were retrieved from our files. All specimens were serially sectioned along the long axis. The size of DCIS was calculated for each case by 2 different methods: (1) mapping method (average thickness of each slice x number of consecutive slices with DCIS) and (2) block method (number of blocks with DCIS x 0.3 cm). Additional calculations were performed by using 0.35, 0.4, and 0.5 cm as multiplication factors for the block method in order to improve concordance. RESULTS: The block method underestimated the size in 71 cases (72%) by 4.5% to 81.3% (mean, 33%). Using 0.4 cm as the multiplication factor improved concordance, while multiplying by 0.5 cm led to an overestimation of size. CONCLUSIONS: Assessment of DCIS size by the block method is inaccurate and underestimates size in most cases (72%), with an average reduction of 33%. Using 0.4 cm as the multiplication factor improves concordance. A standardized method for size estimation is necessary for effective patient management.