The aim of this study was to determine whether it is safe and feasible to perform SLNB in patients with clinically suspicious axillary LN metastasis on preoperative imaging studies. The disease status of the axillary LN is the most significant prognostic factor for patients with breast cancer . SLNB is feasible and accurate, works well in a wide range of practice settings, increases staging accuracy by allowing enhanced pathologic analysis, has less morbidity than ALND, and gives local control comparable to that of ALND . Therefore, ALND for uninvolved axillary LN is considered unnecessary and improper, and indication of SLNB is important. Presently, there was no statistically significant difference in axillary recurrence between SLNB and ALND groups for clinically suspicious axillary LN metastasis (P=0.420). Therefore, SLNB in clinically suspicious patients on preoperative imaging studies might be safe and feasible in the clinical setting.
The NCCN guideline recommends that SLNB should be performed in patients with clinically negative axillary LNs . Still, many authorities consider clinically positive axillary LNs a contraindication for SLNB . Nevertheless, the role of SLNB is increasing and various studies have shown that clinical assessment of axillary LNs alone is inaccurate with a false positive rate up to 40% [11, 18]. In our study, SI patients were regarded as those for whom the preoperative imaging techniques of US, MRI, and PET-CT scanning revealed suspicion of axillary LN. Owing to the low specificity of imaging studies, direct ALND in SI patients could potentially lead to unnecessary ALND.
This study emphasizes the feasibility of SLNB, even in SI patients. More than 60% of all primary operable breast cancers do not have axillary LN metastasis . Non-invasive methods like US, MRI, PET-CT have gained more importance in staging axillary LN. Nevertheless, no imaging study is completely accurate. Axillary US provides additional value in detecting pathological axillary LN [19, 20] but sensitivity has reportedly varied from 26.4% (15.3% to 40.3%) to 75.9% (56.4% to 89.7%) and specificity from 88.4% (82.1% to 93.1%) to 98.1% (90.1% to 99.9%) . A meta-analysis of 25 studies including 2,460 patients reported that PET-CT provided lower sensitivity (37% to 85%) and high specificity (84% to 100%) . The present analysis also indicated that the sensitivity of PET-CT is not sufficient for staging axillary LNs. Also, adding axillary MRI sequentially after axillary US does not significantly improve detection rate of positive nodes . In our study, 56.57% of accuracy (Table 4) was shown with preoperative imaging techniques and false positivity of SI reached 61.23% (218/356) (Table 3). Hence, SLNB in SI patients might be possible.
It is now regarded that a proportion of patients can be spared an SLNB with the aid of preoperative axillary US combined with fine-needle aspiration cytology (FNAC) . Indeed, when FNAC is combined, the likelihood of false positives and false negatives would decrease . However, preoperative axillary US alone is insufficiently specific to obviate the need for SLNB because of the substantial number of false negative results, especially in stage N1 disease, although it may almost exclude N2 and N3 disease . In our study, 52/323 patients (16.1%) who underwent SLNB were proved to have N1 disease. Therefore, preoperative axillary US combined with FNAC alone might have produced false negative results with additional costs. In fact, we tried to perform routine axillary US combined with core needle biopsy but a number of patients (the proportion is not identifiable) refused to perform additional biopsy due to additional pain, cost, and bleeding.
There are some limitations to our study. First, it is a retrospective review of a small number of patients. Further evaluation with a large number of prospective randomized controlled studies must be done in a more standardized group for validation. Second, there were some confounding factors concerning postoperative adjuvant therapies, including radiation, systemic, or endocrine therapies. These factors could have influenced the results. Despite these limitations, the study is significant and is the first to recommend SLNB in SI, based on its demonstrated feasibility and safety.
Our evaluation of SLNB in SI patients with breast cancer suggests that no imaging techniques can replace surgical staging and histologic confirmation of nodal status . Hence the inaccuracy of the imaging techniques allows indications of SLNB widening and SLNB in SI patients is safe and feasible. However, further prospective trials with a larger cohort of patients with long-term follow up are required to verify this observation.