When these data were combined in two meta-analyses, Ansari et al. reported an overall 3.7 % nodal positivity rate while van Deurzen et al. similarly reported the nodal positivity as 4 %; both were for patients with a definitive postoperative diagnosis of pure DCIS [23, 24]. The implications of SLN positivity in pure DCIS require further discussion.

From 1996 to 2006, Intra et al. evaluated 854 patients with pure DCIS who underwent SLN biopsy at the European Institute of Oncology [10]. DCIS with microinvasion was excluded. SLN metastases were discovered in 12 out of 854 patients (1.4 %)—a total of 5 patients with macrometastases, 7 patients with micrometastases, and 4 patients with ITCs (pN0i +). Of the 12 patients with SLN positivity, 11 underwent axillary node dissection but none had additional nodal disease. Other studies [2–5, 19, 25] similarly demonstrate lone SLN positivity after formal axillary lymph node dissection. This questions the value of axillary dissection for pure DCIS with SLN positivity particularly in women with micrometastases or ITCs.

Mabry et al. analyzed 564 patients with pure DCIS who underwent either axillary lymph node dissection or SLN biopsy [19]. Only 2 of 564 patients had positive nodal disease, both in the axillary dissection group. These patients were upstaged, underwent mastectomy followed by systemic treatment, and survived beyond 10 years without local or distant recurrence. Six patients in the axillary dissection group had local invasive recurrences and died from metastatic disease; all six had no evidence of nodal disease at the time of axillary dissection. In addition, of the 171 patients who underwent SLN biopsy, ITCs alone were detected immunohistochemically in 10 patients but only 2 of the171 patients had local recurrence and none developed regional or distant recurrence. Consequently, the authors concluded that lymph node status did not predict poor outcome in patients with DCIS. However, lymph node status may predict which primary tumors have the potential to be upstaged. Treatment of DCIS will not influence long-term disease-specific survival which already approaches 100 %; the focus should remain on eliminating invasive local recurrences. Perhaps, this is what a positive SLN means in the setting of DCIS—the patient has a higher risk of having a missed focus of primary invasion, and thus these patients have the potential to be upstaged and systemic therapy should be considered based on biologic subtype of the invasive component.

Even with invasive local recurrences after DCIS excision, outcomes remain encouraging. Lee et al. analyzed 1236 patients previously treated for pure DCIS in order to examine local invasive recurrence, distant recurrence, and breast cancer-specific mortality [26]. There were 150 local recurrences (87 DCIS and 63 invasive). The overall 12-year breast cancer-specific mortality after mastectomy versus breast-conserving surgery was 0.8 and 1.0 %, respectively. Even in the 63 patients with invasive local recurrence, the 12-year probabilities for metastasis and breast cancer-specific death were 15 and 12 %, respectively. Thus, even for the worst prognostic group of DCIS patients (those with local invasive recurrences), a favorable prognosis with minimal evidence of distant disease prevails and is unlikely to prove fatal. Thus, for DCIS, local control should be the ultimate goal; not improving survival which already exceeds 98 %.