If you need to find and extract tumor into a smaller image use this: http://www.mathworks.com/programs/ip_cd/ is a webinar on using matlab for image processing. It should be enough of an introductory on ways for you to find the tumor and get certain properties of it.
First you need to prepare a dataset for your input. For each sample you need a labels. If you are classiying tumors in lungs, how many types of lung cancers in your dataset? you should make a separate class for each type. This is the first step then you can use any type of CNN net like ALEXNet, etc. Lots of codes available on github.