Search in the Literature for Viral Hepatitis and Hepatocellular Carcinoma in Iran

I read with interest a nice paper by Zidan et al. about viral hepatitis as etiology of hepatocellular carcinoma in Iran and the world (1). They have presented useful information. However, maybe these comments can add some more information specifically about the Iranian literature. They have searched some databases. However, other useful sites like Scientific information Database (SID), Iranian Research Institute for Information Science and Technology (IRANDOC), Iranian Data Bank of Hepatitis Research and Iranian Data Bank of GI Cancer Research, are also available which first two ones are general scientific and two last sites are specific about gastroenterology. Scopus and Web of Science should also be considered. Although, these sites have overlap with mentioned databases in the paper; however, their importance is that they cover some parts of the literature which are not covered by other national or international databases. The importance of these sites is also because of Grey (unpublished/unavailable) literature.