Discordant response to therapy assessed by F18 FDG PET in a stage IV gastro-esophageal cancer. Can FDG PET detect clone resistance?

Learning Objectives 1. Understanding the utility of F18 FDG PET in assessing response to therapy. 2. Exploring the role of F18 FDG PET to modulate treatment. 3. Understanding new molecular targets and resistance to novel biological agents. 4. Understanding how molecular imaging can improve outcomes by detecting novel biological agents resistance.

F18 FDG PET is used daily in staging, restaging and assessing treatment response in various cancers, including gastroesophageal cancer. Various PET radioisotopes have been developed to map specific molecular targets and receptors in the body. However FDG has not been explored in evaluating molecular and biological behavior between different tumoral clones, e.g., primary vs. metastasis or metastasis vs. metastasis, either in initial staging or in the post-treatment phase. We describe the case of a 40 year old male with stage IV gastroespohageal adenocarcinoma with liver and nodal metastatases. FISH analysis for HER 2 status revealed discordance between the primary esophageal tumor (HER2 positive) and a liver metastasis (HER 2 negative). He was treated initially with FOLFOX and bevacizumab. A follow-up FDG PET scan after two cycles revealed a complete resolution of FDG uptake in liver metastases and lymph node metastases, but no change in FDG avidity of the primary esophageal tumor. At 6 months after 12 cycles of FOLFOX and bevacizumab, the patient developed progression of disease at the primary site as well as new peritoneal implants, with on-going disease stability in the liver and nodal metastases, necessitating a change in therapy. FDG PET may be helpful to modulate treatment and to assess discordant response to treatment. FDG could be used in evaluating molecular and biological behavior between different tumor clones - primary vs. metastasis or metastasis vs. metastasis and discordant response to therapy assessed by FDG PET may prompt further molecular investigations. Studies on a large number of patients are required