Changes in Tumor-to-Blood Ratio as a prognostic marker for progression-free survival and overall survival in neuroendocrine tumor patients undergoing PRRT

• Background:Historically, patient selection for peptide receptor radionuclide therapy (PRRT) has been performed by virtue of somatostatin-receptor scintigraphy (SRS). In recent years, somatostatin-receptor positron emission tomography (SSTR-PET) has gradually replaced SRS because of its improved diagnostic capacity, creating an unmet need for SSTR-PET-based selection criteria for PRRT. Tumor-to-Blood-ratio (TBR) measurements have shown high correlation with the net influx rate Ki, reflecting the tumor somatostatin-receptor expression, to a higher degree than standardized uptake value (SUV) measurements. TBR may therefore predict treatment response to PRRT. In addition, changes in semiquantitative SSTR-PET parameters have been shown to predate morphological changes, making them a suitable metric for response assessment.  Methods:The institutional database of the Department of Nuclear Medicine (University Hospital Essen) was searched for NET patients undergoing ≥2 PRRT cycles with available baseline and follow-up SSTR-PET. Two blinded independent readers reported the occurrence of new lesions quantified tumor uptake of up to 9 lesions per-patient using SUV, TBR, and tumor-spleen ratio (TSR). The association between baseline TBR and changes in uptake / occurrence of new lesions with progression-free survival (PFS) and overall survival (OS) was tested by use of a Cox regression model and log-rank test. Results: Patients with baseline TBR in the 1st quartile had a shorter PFS (14.4 months) than those in the 3rd (23.7 months; p=0.03) and 4th (24.1 months; p=0.02) quartile. Similarly, these patients had significantly shorter OS (32.5 months) than those with baseline TBR in the 2nd (41.8 months; p=0.03), 3rd (69.2 months; p<0.01), and 4th (42.7 months; p=0.03) quartile. Baseline to follow-up increases in TBR were independently associated with shorter PFS when accounting for prognostic markers, e.g. RECIST response (Hazard Ratio=3.29[95%CI= 1.62-6.68]; p<0.01). This was confirmed with regards to OS (Hazard Ratio=1.94[95%CI= 1.14-3.32]; p=0.02). Changes in TSR and SUVmean were not associated with PFS or OS. Conclusions: Baseline TBR as well as changes in TBR were significantly associated with PFS and OS and may improve patient selection and morphological response assessment. Future trials need to assess the role of TBR for therapy monitoring also during PRRT, and prospectively explore TBR as a predictive marker for patient selection.

Ämnesord

MEDICIN OCH HÄLSOVETENSKAP  -- Klinisk medicin -- Radiologi och bildbehandling (hsv//swe)

MEDICAL AND HEALTH SCIENCES  -- Clinical Medicine -- Radiology, Nuclear Medicine and Medical Imaging (hsv//eng)

Nyckelord

NETs

PRRT

theranostics

therapy monitoring

DOTATOC PET

Radiology

Radiologi

Oncology

Onkologi

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