IntroductionSentinel node biopsy (SNB) is a minimally invasive technique used to stage the axilla in patients with early breast cancer and is the current gold standard for lobular or ductal breast carcinoma (1-3). However, around 10% of breast tumors belong to other histologic subtypes such as tubular, colloid, medullary, papillary carcinoma, and others. This is a heterogeneous group of malignancies known as special histologic types (SHT) of invasive breast cancer, with variable outcomes, as well as with variable rates of axillary metastases (4, 5).Some authors have advocated that complete axillary dissection (CAD) could be omitted because axillary involvement is uncommon in such tumors. However, the question is whether SNB itself can also be omitted. As the SNB technique keeps improving and consolidating, some authors have shown a higher than expected rate of positive sentinel nodes in this subset (6). This remains an outstanding question for its implication in adjuvant treatment planning. Although SNB morbidity is lower than CAD morbidity, SNB has nevertheless been reported to carry a lymphedema risk of around 10%.Sentinel node biopsy in these unusual subtypes of breast cancer is poorly studied. The series of these patients are short and there are no data on the technical feasibility in this kind of breast cancer.The purpose of this study was to assess the feasibility of sentinel node biopsy in special histologic types of invasive breast cancer. Materials and Methods:Between January 1997 and July 2008, 2253 patients from 6 affiliated hospitals underwent SNB who had early breast cancer and clinically negative axilla. The patients' data were collected in a multicenter database. For lymphatic mapping, all patients received an intralesional dose of radiocolloid Tc-99m (4mCi in 0.4 mL saline), at least two hours before the surgical procedure. SNB was performed by physicians from the same nuclear medicine department in all cases. Results:Of the 2253 patients in the database, the SN identification rate was 94.5% (no radiotracer migration in 123 patients), and positive sentinel node prevalence was 22%. SHT was reported in 144 patients (6.4%) of the whole series. In this subgroup, migration of radiotracer was unsuccessful in 8 patients (identification rate was 94.4%) and SNs were positive in 7.4%. SN positivity prevalence in these tumors was variable across the subtypes. Higher probability of lymphatic spread seemed to be related to tumor invasiveness (20% of positivity in micropapillary, 15% in cribriform subtypes, and 0% in adenoid-cystic). Conclusion:Sentinel node biopsy is feasible in special histologic subtypes of breast carcinoma with a good identification rate. Lower migration rates, however, might be associated with special histologic features (colloid subtype). Complete axillary dissection after a positive sentinel node cannot be omitted in patients with SHT breast cancer because they can be associated with further axillary disease; the reported very low incidence of axillary metastases would justify avoiding...

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