Sentinel lymph node biopsy in patients with a needle core biopsy diagnosis of ductal carcinoma in situ: is it justified?

Background: The incidence of ductal carcinoma in situ (DCIS) has increased markedly with the introduction of population-based mammographic screening. DCIS is usually diagnosed non-operatively. Although sentinel lymph node biopsy (SNB) has become the standard of care for patients with invasive breast carcinoma, its use in patients with DCIS is controversial. Aim: To examine the justification for offering SNB at the time of primary surgery to patients with a needle core biopsy (NCB) diagnosis of DCIS. Methods: A retrospective analysis was performed of 145 patients with an NCB diagnosis of DCIS who had SNB performed at the time of primary surgery. The study focused on rates of SNB positivity and underestimation of invasive carcinoma by NCB, and sought to identify factors that might predict the presence of invasive carcinoma in the excision specimen. Results: 7/145 patients (4.8%) had a positive sentinel lymph node, four macrometastases and three micrometastases. 6/7 patients had invasive carcinoma in the final excision specimen. 55/145 patients (37.9%) with an NCB diagnosis of DCIS had invasive carcinoma in the excision specimen. The median invasive tumour size was 6 mm. A radiological mass and areas of invasion,1 mm, amounting to "at least microinvasion'' on NCB were predictive of invasive carcinoma in the excision specimen. Conclusions: SNB positivity in pure DCIS is rare. In view of the high rate of underestimation of invasive carcinoma in patients with an NCB diagnosis of DCIS in this study, SNB appears justified in this group of patients.