Systematic literature review question doubt

There are as of now quite a decent number of R library to run meta-analysis. This paper is one of the many which i have seen. Now the fundamental question which I would like to know is as shown in this paper.

For example if I am looking at the efficacy of two drug on overall survival in certain disease. So I will have to look for literature where studies on same cancer but two different drug and in those studies the overall survival is reported whichever paper I will have to take.

Is this the right way of doing it or my approach is not correct?