OSNA for colon cancer staging

Specialist commentator comments

The specialist commentators noted that the OSNA system can be used to analyse the whole LN, which may be an advantage compared with conventional histopathology. OSNA has the potential to be highly promising for colon cancer staging as either a replacement or adjunctive technique. OSNA may increase the sensitivity of detecting LN metastases compared with conventional analysis and could increase the number of people who would benefit from chemotherapy. People with metastases that are not detected with conventional analyses are currently undertreated. One commentator noted that being able to assess whole LNs may be a useful adjunct in detecting occult tumour cells (that are defined by the presence of LN metastases with an unknown primary tumour). The presence of occult tumour cells is an important prognostic variable, but can be overlooked by conventional histopathology.

The specialist commentators raised several concerns about the potential benefits of OSNA. The benefit for people whose cancer has been upstaged by OSNA cannot be assumed to be the same as for people whose cancer was conventionally staged as LN positive and needs prospective assessment. Extracapsular LN involvement is becoming a significant prognostic factor, but this would not be detected by OSNA. In this context, 1 commentator suggested that although useful, particularly for assessing sentinel LNs, OSNA should not replace detailed histological analysis.

The specialists noted that the evidence base for OSNA in colon cancer is limited. One commentator suggested that the upstaging of colon cancer based on OSNA results could be related to detecting micrometastasis rather than macrometastasis, and questioned the benefit of detecting micrometastasis. The clinical role of micrometastasis seems unclear and so the effect on patient care has yet to be shown. If OSNA is mainly detecting micrometastasis and performs similarly to intensive histopathology with immunohistochemistry as shown in 1 of the studies, then this may be the more appropriate comparator (as opposed to conventional histopathology). One specialist noted a growing number of studies showing that marker genes (such as cytokeratin‑19) for metastatic cells in LNs in colorectal cancer are better than conventional histology using haematoxylin and eosin staining, suggesting that using cytokeratin‑19 mRNA is a valid method of cancer staging.

One specialist commentator noted that OSNA did not seem to be overly expensive and carried no risk for patients. However, another commentator suggested that the cost of offering the OSNA test to all patients with early colon cancer would be unjustifiable without stronger evidence showing that the test would have an effect on outcome for patients. If OSNA only detects a small proportion of people with LN macrometastases, then the cost–benefits of investment also need consideration.

Long-term trials would be needed to look at overall survival in patients tested using OSNA compared with current standard techniques. The primary measureable benefit of OSNA would be in the improved survival of patients whose cancer had been upstaged. More subtle aspects, such as toxicity and quality of life, would also be ideally assessed.