Mixed response refers to a situation in which some metastases are responding and others are growing and/or new metastases are appearing in the same time. It is a reflection of tumor heterogenity – some cells respond to therapy and others do not. A commonly used definition when precision is required, such as in clinical studies, is that it is defined as >30% difference in individual lesion response, with all lesions showing a similar behavior; true mixed response (TMR) as two lesions showing progression versus response; homogeneous response (HR) is similar behavior of all lesions. Mixed respnses are quite common in colorectal cancer; in one study of liver metastases, mixed responses were found in 30% of the patients(1). Unfortunately, this metric has been somewhat neglected and is not often included in clinical studies(2). As such, there had been little research and no guidelines to the oncologists on how to handle the mixed response situation. There appears to be a consensus that whether to change therapy depends on other available options, degree of security that the lesions that progressed truly progresses (as opposed to swelling or inflammation; some physicians advocate rebiopsy in unclear cases) and the number and size of non-responsive lesions.
1.van Kessel CS, Samim M, Koopman M, van den Bosch MA, Borel Rinkes IH, Punt CJ, van Hillegersberg R.
Radiological heterogeneity in response to chemotherapy is associated with poor survival in patients with colorectal liver metastases. RECIST, Chemotherapy, ResponseEur J Cancer. 2013 May 18. pii: S0959-8049(13)00261-X. doi: 10.1016/j.ejca.2013.03.027. [Epub ahead of print]
2.E.A. Eisenhauera et al, New response evaluation criteria in solid tumours: Revised RECIST guideline (version 1.1), EUROPEAN JOURNAL OF CANCER 4 5 ( 2 0 0 9 ) 2 2 8 –2 4 7
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