Feasibility of omitting sentinel lymph node biopsy in an under-screened cohort of breast cancer patients with a pre-mastectomy diagnosis of ductal carcinoma in situ

Background Nodal involvement in ductal carcinoma in situ (DCIS) is rare. In patients with DCIS diagnosis prior to mastectomy, a sentinel lymph node biopsy (SLNB) is usually performed during mastectomy, to avoid the risk of reoperation and the non-identification of SLN subsequently, should there be an upgrade to invasive cancer. We aimed to study the feasibility of omitting SLNB in an under-screened cohort, with mostly symptomatic patients and DCIS diagnosis before mastectomy, by determining the upgrade rate to invasive cancer/ DCIS microinvasion (DCISM) and its associated risk factors. Methods Patients with pure DCIS diagnosis pre-mastectomy were reviewed retrospectively. Patients with known DCISM or invasive cancer before mastectomy and bilateral cancers were excluded. Patients’ demographics, radiological and pathological data pre-mastectomy were analysed. Results 189 patients were included. The mean age was 53.8 (range: 29-85) years old. 64.4% presented with symptoms. 36.0% and 15.3% upgraded to invasive cancer and DCISM on mastectomy respectively. Palpable tumour (p=0.0036), large size on ultrasound (p=0.0283), tumour seen on mammogram and ultrasound (p=0.0082), ultrasound-guided biopsy (p<0.0001), high grade DCIS on biopsy (p=0.0350) and no open biopsy/lumpectomy before mastectomy (p<0.0001) were associated with upgrade, with the latter factor remaining significant after multivariable analysis. Nodal involvement was 8.47% and was associated with invasive cancer (p<0.0001). Conclusion In a cohort who had DCIS diagnosis before mastectomy and were mostly symptomatic, the upgrade rate was 51.3%. Despite the high upgrade rate, nodal involvement remained comparable. Risk factors could select patients for omission of upfront SLNB, with a delayed SLNB planned if needed. Micro-abstract In this single centre retrospective cohort study (n=189), we investigated the feasibility of omitting sentinel node biopsy in patients diagnosed with ductal carcinoma in situ (DCIS) undergoing mastectomy. The upgrade rate to micro-invasive and invasive cancer in our cohort is 51.3%. Despite the high upgrade rate, nodal involvement remained low at 8.47%. Risk factors for upgrade could be used to select patients for omission of upfront SLNB.