The accurate evaluation of a patient’s response to cancer treatment is an important part of any therapeutic plan, but this is especially true for people being treated for malignant mesothelioma. It is an aggressive malignancy that often presents with a poor prognosis. Pleural mesothelioma, the most common form of the disease, is typically diagnosed only in its advanced stages and the median survival time for these patients is often less than one year from diagnosis. For these patients, a physician’s ability to quickly and accurately gauge an individual’s response to mesothelioma treatment could have profound implications for his or her future health.

Historically, however, this has been a difficult venture for physicians. As is often the case with this disease, mesothelioma presents unique challenges in determining treatment response. Because of its diffuse growth pattern, mesothelioma is not efficiently analyzable by World Health Organization response criteria, which focuses on tumors with bi-dimensionally measurable diameters. RECIST (response evaluation criteria in solid tumors) criteria have been semi-successfully applied in the evaluation of mesothelioma, but, again, the disease’s distinct growth pattern make site selection in the determination of a change in tumor spread a difficult endeavor, so modified RECIST criteria specific to mesothelioma was developed and is now generally in use.

CT has traditionally been the imaging technique of choice for mesothelioma diagnosis and response evaluation, although a number of studies have demonstrated that MRI provides enhanced resolution for diagnostic purposes. Many physicians feel its greater resolution could also be useful in tracking treatment response, but MRI’s use for the evaluation of response criteria has not been studied until quite recently, so there wasn’t any published data to draw a conclusion from. However, the situation has now changed: the results from the first study have now been released and they clearly show a benefit to the use of MRI.

Overview of the Study

Researchers from Germany enrolled 50 patients with proven pleural mesothelioma into their study. There were 32 males and 18 females, with a mean age of 59 years old. None of the patients received any treatment prior to the chemotherapy regimen the study employed. The plan of the study was to compare the efficacy of RECIST and modified RECIST criteria using CT and MRI in determining early patient response to treatment (chemotherapy, in this case).

After patients enrolled in the study, they underwent at least four sets of CT and MRI scans:

1. Before treatment.
2. After three cycles (out of six) of chemotherapy.
3. 4 weeks after the second scan.
4. After the six cycles were completed.

The comparison between CT and MRI using RECIST and modified RECIST took place after the 2nd set of scans were taken (three cycles into therapy).

Results

Using a volumetric analysis, i.e., change in gross tumor volume, 28 patients demonstrated a partial response to therapy, 12 demonstrated stable disease and 10 patients experienced progressive disease. MRI using the modified RECIST criteria correctly identified patient response in all cases, while the use of traditional RECIST criteria correctly identified it in only 46 cases. CT using the modified RECIST criteria correctly identified treatment response in 48 cases, but only in 44 cases when using the unmodified RECIST criteria. The authors note that CT demonstrated a tendency to underclassify therapy response.

The authors report that in dividing the patients into groups of those who responded to treatment with those who did not respond, the former group demonstrated a median survival figure of 15.1 months, while the non-responding group had a median figure of only 8.9 months. When comparing the early response evaluation scans taken after the third chemo cycle with those taken after the last cycle, they didn’t find any change between those who responded and those who did not respond. The authors speculate that early response results may then be used to infer who will respond to treatment and who will not, which should allow earlier changes and/or optimizations to treatment plans for those who are responding, as well as the avoidance of useless therapy or side effects in those who are not.

Conclusion

The authors recommend the use of MRI with modified RECIST criteria in the evaluation of early therapy response in patients with malignant mesothelioma. CT with modified RECIST may be recommended for some patients, but they state (and have shown) that MRI returns more precise results. This study, should its findings be independently confirmed, has important implications for the evaluation of patient response to therapy, as it suggests that physicians can evaluate treatment response at an earlier point than they normally do. With aggressive diseases such as pleural mesothelioma or peritoneal mesothelioma, accurate and early evaluation can help patient and physician alike make better, more informed decisions.

Labels: mesothelioma