Radiologic f/u for melanoma patients with stable diease - CT or PET????

The best radiologic evaluation of melanoma patients' disease status/progression and how to interpret those results has been one of the many adjustments needed among researchers, oncologists and radiologists since use of immunotherapy began.  Pseudoprogression, tumors that stop growing but don't go completely away, development of pneumonitis and lung nodules - are just a few of the many problems that have had to be considered.  Here is an earlier post that discussed how researchers were looking at these issues:  Radiological evaluation of response to melanoma treatments

Now there is this ~

Stable disease or complete response? A critical evaluation of the radiologic response to immune checkpoint blockade in advanced melanoma. Tietze, Heppt, Angelova, et al.
Hautarzt. 2017 Apr 5. 

Rating the response of melanoma to immune checkpoint blockade (ICB) by conventional CT proves to be difficult, since response patterns and kinetics differ from the classical responses seen with other therapies. Hence, immune-related response criteria were developed. However, they are mainly based on the alteration of the diameter of lesions over time but do not include metabolic activity.

The aim of this study was to search for additional criteria to improve the interpretation of the radiologic images of patients with metastatic melanoma after ICB.

We retrospectively analysed 7 patients with metastatic melanoma over a period of 13-41 months after treatment with ICB using contrast enhanced CT scans from the neck region to the lower abdomen and compared the results in the follow ups with ¹⁸F-FDG PET/CT.

Metastatic lesions in 5 of 7 patients rated as stable disease (SD) in CT staging showed no metabolic activity in ¹⁸F-FDG PET/CT. The size of these lesions did not increase or show metabolic activity in the further follow-up, even after discontinuation of ICB. In contrast, tumor lesions in the other 2 patients rated as SD in CT staging showed metabolic activity in ¹⁸F-FDG PET/CT. These tumor lesions expanded significantly in the further course of the disease.

In addition to the size of a tumor lesion, its metabolic activity adds important information regarding treatment response. Thus, we propose that the metabolic activity assessed with ¹⁸F-FDG-PET/CT should be included in the immune response criteria. No FDG uptake in a lesion should be rated as inactive tumor rather than SD and further treatment may not be required.

Given this report, if I were a patient with stable disease on CT....I would want a PET to look for FDG uptake.  No uptake????  THEN I would consider myself with stable disease and feel much better about going off therapy!!!  For what it's worth! - c