CREBBP Mutation as a Culprit for Negative SSTR2 PET in Neuroendocrine Tumors

This study aimed to elucidate the molecular and genetic factors contributing to negative ⁶⁸Ga-DOTATATE PET imaging in neuroendocrine tumors (NETs). By integrating whole exome sequencing (WES) and single-cell RNA sequencing (scRNA-seq), we sought to unravel the interplay between negative results of ⁶⁸Ga-DOTATATE PET and genetic mutations in NETs.

A total of 18 patients with lung, ileal, or pancreatic NETs who underwent ⁶⁸Ga-DOTATATE and ¹⁸F-FDG PET/CT scans as part of their initial diagnostic workup were retrospectively reviewed. WES analysis was conducted to investigate the genetic profile of circulating tumor cells of patients with negative ⁶⁸Ga-DOTATATE scans. Leveraging scRNA-seq and single-cell somatic variant calling analysis, we compared the mutation burden and genetic hallmarks of NET cells with high /positive SSTR2 expression to those with negative/low SSTR2 expression.

Our analysis identified an association between negative ⁶⁸Ga-DOTATATE scans and reduced survival rates, regardless of tumor grade. WES highlighted a predominance of missense mutations, including CREBBP mutation, particularly in patients with negative PET results (incidence of %67 vs. %0). We observed a deleterious mutation in the SSTR2, likely accounting for the observed negative PET scans (incidence of %33). Single-cell single nucleotide variant (SNV) analysis showed that the total unique mutation burden in cells with negative/low SSTR2 expression was significantly higher compared to cells with positive/high expression; and notably, the CREBBP mutation was observed in more than 50% of patients and approximately 35% of NET cells. These results indicate that the frequency of CREBBP mutations is nearly as high as other well-known NET mutations such as MEN1, PTEN, and RB1. Additionally, CREBBP mutations are significantly more frequent in tumors with negative/low SSTR2 expression.

This study suggests that CREBBP mutations in NETs may potentially alter SSTR2 expression, indicating that patients with the mutated CREBBP genotype may not be suitable candidates for SSTR2-targeted PET imaging and radionuclide therapy.