Think hundreds if not more different pathways utilizing many different mechanisms that are not even mapped that well. Anything from external to the cell molecul

Think hundreds if not more different pathways utilizing many different mechanisms that are not even mapped that well. Anything from external to the cell molecules to internal ones to noise based ones. And then add on top of that variations in tumor topography and variations in each tumor type that make some people with the same cancer react to a drug really well while others don't. Also no categorization in medicine is arbitrary ( or at least almost none). Everything on a clinical level is categorized based either on how it's best diagnosed or cured, for example a cancer might be categorized as a small cell lung cancer when it comes to chemo but use a different classification scheme from radiologists when surgeons are concerned because they care about the area of effect instead ( in both cases a cure based taxonomy). The small cell cancer has different molecular signatures than e.g. non small cell types which means it will react differently on specialized antibody therapies. This taxonomy is nowadays expanding rapidly based on new drugs and studies on which variations of proteins they are effective.