Malignant pleural mesothelioma (MPM) is a challenging cancer to treat for many reasons, one of which being the difficulty in assessing whether there has been any meaningful change in the volume of a cancer that doesn't tend to appear as a discrete mass, but most commonly as thickening of the pleura, the lining around the lung that is normally a thin, onion skin, but can thicken to be more like an orange rind or even thicker. We can often see this pattern in some people with lung cancer who happen to have a form of the disease that also primarily appears as pleural-based deposits of cancer.
Here's a brief video that explains my approach to a so-called "mixed response" to treatment for a lung cancer.
There isn't a formal teaching or "best answer" about how to approach this issue, but what I explain here is a common and I think very sensible strategy for a still controversial clinical setting (if I do say so myself). I'd welcome your comments.
I hope you find it helpful if you or someone you care about faces this situation.
As I described in a post last year, one of the common features of angiogensis inhibitors is that lesion often cavitate, shrinking not only from the outside in, but hollowing out and dying from the inside out.