The sentinel node study by the OSNA method is being applied in an increasing number of hospitals. Its advantages over the traditional approach with haematoxylin-eosin and immunohistochemistry (HE/IHC) include the decrease in the workload for the pathologist as the process is largely automated and the ability to analyse the full node instead of just some sections while performing surgery of the primary breast tumour.
Different studies have shown that the OSNA assay has a good correlation with the pathological study (Tsujimoto et al. 2007; Sagara et al. 2011; Li et al.; Tamaki et al. 2009), and it also has a higher sensitivity for the detection of micrometastases (Osako et al. 2011).
In our series we have found a similar rate of macrometastases in SLN analysed by OSNA and HE/IHC but with an increased detection of micrometastases with OSNA.
However, this increase in the number of nodes with micrometastases provides information that is difficult to apply in the clinical setting, as its prognostic value has not been fully clarified. One of the most relevant studies to address this issue is the prospective NSABP B-32 trial, which was designed to evaluate the outcome of SLN biopsy alone compared to axillary dissection, in which 5,611 patients with SLN biopsy were randomized to undergo or not to undergo axillary clearance (Krag et al. 2007). Subsequently, an analysis was published of patients with occult nodal metastases reviewing almost 4000 ganglion blocks (Weaver et al. 2011). At five years, the presence of occult metastases was associated with a lower overall survival, progression free survival and distant metastases free interval compared to node-negative patients. Although this increased risk in the three parameters was statistically significant, the magnitude of the difference in the 5-year Kaplan-Meier estimates of overall survival was only 1.2 percentage points and the authors concluded that this difference might be of little clinical relevance.
The finding of micrometastases in the sentinel node can have an impact on clinical management. In our series all patients with micrometastases in the OSNA group underwent axillary clearance. One of the reasons why it was done was the study of a possible involvement of other lymph nodes, which is estimated to occur in approximately 10-15% of cases of SLN biopsy micrometastases in classical histological studies (Solá et al. 2013; Galimberti et al. 2013; Cserni et al. 2004; Houvenaeghel et al. 2009). In this sense, we cannot draw conclusions from our data since the rate of micrometastases in the HE/IHC group was very low and barely any lymphadenectomies were performed. Published data about the OSNA technique also indicate that the PCR load of cytokeratin 19 correlates with the finding of non-sentinel node metastases (Osako et al. 2011), although in our sample none of 17 patients undergoing lymphadenectomy due to micrometastasis in OSNA had involvement in the other nodes.
Despite the possible presence of other affected lymph nodes there are trials showing that lymphadenectomy can be omitted in patients with micrometastases in the SLN biopsy since their presence does not increase the rate of axillary recurrence (Solá et al. 2013; Galimberti et al. 2013; Guenther et al. 2003; Gant et al. 2003; Langer et al. 2005). Recently, two randomised trials that explore this issue had been published, a Spanish study (Solá et al. 2013) and the IBCSG 23–01 trial (Galimberti et al. 2013). With a recruitment lower than expected, 247 and 932 patients respectively with micrometastases in SLN biopsy were randomly assigned to axillary dissection or no axillary dissection. No differences in terms of disease-free survival after a follow-up of five years were seen.
Probably the long-term monitoring of patients in which micrometastases are detected by OSNA will provide new data in this sense, as it is a method that is more reproducible and allows a more complete analysis of the node than the histopathological analysis (Osako et al. 2011; Tamaki et al. 2009).
Currently in our centre micrometastases in SLN biopsy are not considered an indication for axillary clearance, given the growing literature that supports this decision and the recommendations in this sense of the 2011 St Gallen Consensus Conference (Goldhirsch et al. 2011). We maintain the indication in case of macrometastases although in the future this might be avoided in cases of macrometastases in only one or two sentinel nodes in certain patient, based on the findings of the ACOSOG Z0011 study (Giuliano et al. 2011).
In any case, the full analysis of lymph nodes by OSNA allows us to perform lymphadenectomy in the same surgical procedure in all cases, something not always possible in patients studied by IHC in which the full results can be obtained later. The performance of a single procedure can provide important advantages for the patient, such as avoiding a second operation and a possible delay in the start of adjuvant therapy, as well as lower cost for the institution (Guillen-Paredes et al. 2011).