Improving the sensitivity of stereotactic core biopsy to diagnose ductal carcinoma in situ of the breast: a mathematical model

Stereotactic core biopsy (SCB) is performed on mammographically suspicious, nonpalpable lesions of the breast. Reported sensitivities of SCB for the d etection of ductal carcinoma in situ (DCIS) vary from 41% to 93%. We have d eveloped a simple mathematical model to predict the probability of retrievi ng at least one diagnostic core from a focus of DCIS. We make recommendatio ns of the number of samples needed for different sized areas of microcalcif ication. The sensitivity of SCB is affected by needle placement accuracy, d iameter of the area of microcalcification (d), histological density of DCIS (x) (calculated as 7.5% by previous studies) and number of core samples (n ) removed. The probability of achieving at least one representative core su fficient for diagnosis (P-(core)) is defined as: P-(core) = 1 - (1 + rho{[l - (x/100)](d) - 1})(n), where rho is the probability of a SCB accurately t argeting the area of microcalcification. At least seven core samples should be removed in small foci (<5 mm) of DCIS to achieve a 0.75 probability of an accurate diagnosis. The probability of a diagnostic biopsy of larger are as of DCIS (> 10 mm) is 0.95 when five cores are removed. This formula serv es as an explanation to patients why SCB may fail to diagnose DCIS, and jus tifies the retrieval of more core samples to increase the probability of an accurate diagnosis and to reduce the chance of a non-representative core. In the absence of sufficient samples, a wire-guided open biopsy is necessar y to exclude DCIS.