A noteworthy and provocative article by Dowlatshahi et al. in this issue of Cancer describes a preliminary study assessing the incidence of occult metastases in the sentinel lymph nodes (SLNs) of patients with small breast carcinomas. 1 SLNs from 52 patients whose primary tumors had a mean greatest dimension of only 1.35 cm were evaluated microscopically in a comparison of routine hematoxylin and eosin (H & E)-stained slides, sectioned at 2 mm intervals, and slides sectioned serially at 0.25 mm intervals and immunostained for cytokeratin (an epithelial marker). The entire SLN sample from each patient (an average of 1.5 lymph nodes per patient) was evaluated. Metastases were found in the SLNs of 6 patients (12%) when examined by H & E staining and in 30 patients (58%) when examined by immunohistochemistry (IHC). Of the additional 24 patients with positive SLNs identified by IHC alone, half of them had lymph nodes that were involved by minute clusters of tumor cells (defined as ฯฝ10 cells), whereas the remainder had more substantial but still generally small tumor implants. The unexpectedly high rate of occult micrometastases in patients with such small primary tumors raises a number of perplexing issues.
Today, nearly all patients with potentially curable invasive breast carcinoma have most of their axillary lymph nodes (ALNs) excised, primarily for staging rather than therapeutic purposes. ALN status is the most powerful prognostic factor in breast carcinoma and plays a central role in the decision-making regarding subsequent treatment, such as the use of adjuvant systemic therapy. Unfortunately, extensive axillary dissection causes arm pain, arm edema, and limitation of motion in a significant proportion of patients. These problems, coupled with the overall relatively low rate of ALN positivity, have motivated research into less debilitating but, hopefully, equally useful procedures, such as SLN excision. The idea behind the SLN procedure is that the first lymph nodes in the lymphatic drainage from a tumor are the most likely to contain metastases, and the surgery required to remove them is limited and better tolerated than complete ALN dissection. Now, in experienced hands, the ability to identify SLNs and the sensitivity of SLNs for axillary metastases are both well over 90%. [2][3][4] This procedure is already replacing standard axillary dissection in some centers, even though its clinical utility has still not been demonstrated in prospective randomized trials. As with any proce-