Background: When microinvasion cannot be ruled out on core needle biopsy (CNB) in the setting of ductal carcinoma in situ (DCIS), the surgeon must decide whether to perform a sentinel lymph node biopsy (SLNB) at the time of surgery. Up to 10 % of patients with T1mi have nodal disease, but the utility of SLNB in DCIS suspicious for microinvasion (Smic) is unclear.
Methods: The University of Chicago pathology database was queried for a diagnosis of Smic or definite microinvasion (Mic) on CNB from 2000 to 2014. We analyzed histology, imaging, core needle size, and the use of myoepithelial immunohistochemistry (IHC) markers.
Results: We identified 103 women, 72 with Smic and 31 with Mic on CNB. After surgery, 32 % of Smic patients had infiltrating ductal carcinoma (IDC). Seventy-two percent of Smic patients underwent SLNB, with 67 % performed at the initial surgery. SLNB was positive in 6 % and 10 % of Smic and Mic patients, respectively (p = 0.66). Excluding N1mic, the incidence of macrometastatic nodal disease was 1.9 % for Smic patients and 3.3 % for Mic patients (p = 1.00). For Smic patients, IDC was associated with a larger lesion size and smaller CNB needle. In the setting of Smic, grade, necrosis, or presence of a mass did not increase the risk of IDC.
Conclusions: In patients with Smic on CNB, the incidence of macrometastatic nodal disease after SLNB is rare. Surgeons may consider omitting SLNB until IDC is definitively confirmed, especially in patients with Smic apart from other high-risk features.