How do oncologists determine whether someone is responding to cancer treatment?
It's a complicated and challenging science to try and objectify data from clinical studies. We now use various qualitative and quantitative measures, such as tumor shrinkage, to ascertain treatment benefit. And response is measured differently in solid tumors than it is in hematologic, or blood, malignancies such as leukemia.
How is response measured in patients who have solid tumors such as breast cancer?
For patients with existing disease, often those with metastatic cancer, what is evaluated is so-called objective response. There are now internationally recognized criteria called the RECIST (Response Evaluation Criteria in Solid Tumors) criteria. According to the RECIST guidelines, a partial response, for example, is defined as a 50 percent decrease in the perpendicular diameter of a tumor mass. Often the tumors are at least round-like; they can be measured in one dimension on a CAT scan, for example.
We've learned that a partial response correlates with improvement in quality of life for the patient, such as improvements in pain, performance status, weight gain or improved lung function, if it happens to be a lung cancer, or improved intestinal function, if someone has intestinal metastases.
Then there are examples of complete responses, and those can either be clinical or pathological. If you do a CAT scan or MRI and you don't see cancer, that's a clinical response. A pathologic complete response is when, during surgery, no cancer is found.
