Sandostatin LAR therapy differentially alters 68Ga-DOTATATE uptake in normal tissues compared to primary tumors and metastatic lesions

Abstract

Synthetic somatostatin analogs have been posed as a potential source of error in somatostatin receptor imaging by interfering with tumor detection; however, experimental models and clinical studies have shown a complex mechanism of octreotide effect on tumors. This study aimed to assess whether 68Ga-DOTATATE uptake differs before and after treatment with long-acting somatostatin analogs. Methods: Thirty patients with intermediate to well differentiated neuroendocrine tumors (NET) who underwent 68Ga-DOTATATE Positron Emission Tomography/Computed Tomography (PET/CT) scanning before and after receiving long-acting repeatable (LAR) Sandostatin were included in the study. The maximum and the mean standardized uptake values (SUVmax and SUVmean) of healthy target organs, residual primary tumor and up to five lesions with the highest SUVmax in each organ were compared before and after octreotide treatment. Results: Thirty patients (15 males) with a mean age of 64.6±13.4 years were studied. The mean time interval between the two 68Ga-DOTATATE studies was 9.6±7.2 months, and the mean time gap between the last Sandostatin LAR injection and the second 68Ga-DOTATATE study was 25.1±14.8 days. The pre-treatment mean SUVmax and SUVmean were both significantly higher in the thyroid, liver and spleen (P<0.05) than the values measured after administration of Sandostatin LAR. No significant differences were found among the uptake indices for residual primary tumor or any metastatic lesions of the liver, bone, lung or lymph nodes before and after Sandostatin LAR administration (P>0.05). Conclusion: Long-acting octreotide treatment diminished 68Ga-DOTATATE uptake in the liver, spleen, and thyroid gland but did not compromise tracer uptake in residual primary tumor and metastatic lesions. These findings have direct impact on the interpretation of 68Ga-DOTATATE PET/CT scans.