Search strategies to obtain evidence for cancer classification

<ns3:p> Background The accuracy of the WHO classification of tumours (WCT), and hence cancer diagnosis, depends on rigorous assessment of the scientific evidence available which describes the defining characteristics of each tumour type. The scale of the task is considerable, given the vast number of publications in the field. The WCT Evidence Gap Map project (WCT EVI MAP; <ns3:ext-link xmlns:ns4="http://www.w3.org/1999/xlink" ext-link-type="uri" ns4:href="https://wct-evi-map.iarc.who.int/">https://wct-evi-map.iarc.who.int/</ns3:ext-link> ) is designed to answer this need, using Evidence and Gap Map (EGM) methodology to inform the WCT, which is well suited to large datasets. Methods As examples to test the strategy, we chose sebaceous carcinoma and cholangiocarcinoma. As a rare tumour, sebaceous carcinoma has a relatively small literature, while the landscape for cholangiocarcinoma is more complex due to recent changes in the classification, the use of outdated terms, and many publications. Results The search strategy uses two components - the first describing the tumour type, including alternative terminology, and the second the tumour characteristics (aetiology, pathogenesis, clinical features, epidemiology, histopathology, etc.), with synonyms, as used in the WCT. Conclusions The results emphasise how relatively small differences in the exact terms and fields searched can produce big differences in the results obtained. It is often important to use a wide range of alternative terms and to cover multiple variations of phrases (via techniques such as proximity searching) to ensure comprehensive results. Limiting results to those characteristics used to classify tumours and using date thresholds helps to improve the relevance of the literature identified. </ns3:p>