As an expert in Oncolytic Virotherapy Professor Cerullo is ranked no: 13 in the world.
The founder of Expertscape believes that no one is an expert at anything unless they are investigating the leading edge of knowledge and are writing about it. So, Expertscape bases its rankings on scientific publications.

For any given topic, Expertscape follows these steps:

It searches the PubMed database to find all the medical journal articles published about the topic in the past ten years.
It assigns a score to each article, based on the article's year of publication (recent is better), the article's type (guidelines and reviews, for example, count more than letters to the editor), and the journal in which the article appeared (some journals are better than others).
It assigns a score to each author of the article (first author scores higher than second author).
It determines the institution, if possible, from which the article appeared.
It tallies the scores for all articles, authors, institutions, cities, regions, and countries, and then graphically outputs the results on web pages.
Thus, Expertscape's rankings are 100% objective, with no elements of a popularity contest, nor any way for an institution to spin marketing dollars into a higher ranking.

Furthermore, the experts listed by Expertscape have demonstrated their expertise by putting their knowledge on paper and getting it through the rigorous review process that characterizes scientific publication.