Does lanreotide (somatostatin analogue) increase the avidity of liver metastases (mets) on positron emission tomography (PET) scans?

Effect of Lanreotide on Liver Metastases Avidity on PET Scans

Lanreotide does not decrease the avidity of liver metastases on PET scans; in fact, it may slightly increase tumor uptake while decreasing normal organ uptake, resulting in improved tumor-to-liver contrast ratios. 1

Mechanism and Imaging Considerations

Lanreotide is a somatostatin analogue that binds to somatostatin receptors (SSTRs) expressed on neuroendocrine tumors (NETs). There has been a longstanding concern that lanreotide therapy might interfere with somatostatin receptor imaging by competing for the same receptors that radiotracers like 68Ga-DOTATATE target.

Impact on PET Scan Results:

• Tumor uptake: Contrary to previous assumptions, lanreotide administration actually leads to a small but statistically significant increase in 68Ga-DOTATATE uptake in tumor lesions 1
• Normal tissue uptake: Lanreotide decreases uptake in normal organs including liver, spleen, and thyroid 1
• Tumor-to-liver ratio: The net effect is an improved tumor-to-liver ratio, which enhances the visibility of liver metastases 1

Clinical Implications

Current Practice Guidelines

The NCCN guidelines recommend somatostatin receptor-based imaging (such as 68Ga-DOTATATE PET/CT) for patients with NETs to:

• Assess sites of metastases
• Determine somatostatin receptor status before treatment with lanreotide or octreotide 2

Key Considerations for Imaging Protocol

• No need for medication withdrawal: The 2019 prospective intra-patient study strongly suggests that discontinuation of lanreotide injections prior to 68Ga-DOTATATE PET examinations is unnecessary 1
• Timing of scans: PET scans can be performed even one day after lanreotide injection without compromising imaging results 1

Prognostic Value of PET Imaging

• Tumor-to-liver ratio (TLR) determined by 68Ga-DOTA-TOC PET/CT has been identified as an independent prognostic factor for progression-free survival in patients treated with lanreotide 3
• Patients with higher TLR (≥8.1) have better outcomes with lanreotide therapy than those with lower TLR values 3

Practical Applications

For patients on lanreotide therapy requiring PET imaging:

1. Continue lanreotide therapy as scheduled
2. No need to delay PET imaging after lanreotide administration
3. The slightly enhanced tumor-to-liver ratio may actually improve detection of liver metastases

Potential Pitfalls

• While lanreotide doesn't negatively impact imaging, be aware that different NETs have varying levels of somatostatin receptor expression
• High-grade (G3) NETs may have lower somatostatin receptor expression and might be better visualized with FDG-PET 2
• For comprehensive staging, consider complementary imaging modalities as recommended by guidelines 2

In conclusion, lanreotide administration does not compromise the quality of somatostatin receptor-based PET imaging for liver metastases and may even slightly enhance tumor visibility through improved tumor-to-liver contrast.