Is a Positron Emission Tomography (PET) scan beneficial in diagnosing renal cancer?

From the Guidelines

Positron Emission Tomography (PET) scans are not recommended as a first-line imaging modality for diagnosing renal cancer, and instead, contrast-enhanced CT scans, MRI, and ultrasound should be used as the initial diagnostic imaging studies. The limited utility of PET in renal cancer diagnosis is partly due to the variable metabolic activity of renal tumors and the normal excretion of the radiotracer through the kidneys, which can obscure lesions 1. Additionally, some renal cancers may not demonstrate significant uptake of the radiotracer (typically FDG), leading to false-negative results.

Key Points to Consider

• The European Association of Urology guidelines on renal cell carcinoma suggest that PET is not a standard investigation in patients with clear-cell RCC, but it may be useful in specific cases such as papillary RCC 1.
• The National Comprehensive Cancer Network (NCCN) guidelines also state that PET alone is not a tool that is standardly used to diagnose kidney cancer or follow for evidence of relapse after nephrectomy 1.
• Other studies have shown that PET scans may have some utility in evaluating metastatic disease, assessing treatment response, or in cases where conventional imaging is inconclusive 1.
• However, the American College of Radiology (ACR) Appropriateness Criteria do not recommend FDG-PET/CT for the surveillance of patients after surgical excision of RCC, although emerging data suggest that FDG-PET can be useful for detecting metastatic or recurrent RCC 1.

Recommendations for Practice

• For patients with suspected renal cancer, a contrast-enhanced CT scan or MRI should be pursued as the initial diagnostic imaging study rather than a PET scan.
• PET scans may be considered in specific scenarios such as evaluating metastatic disease, assessing treatment response, or in cases where conventional imaging is inconclusive.
• The use of other PET tracers, such as 11C-choline, 18F-sodium fluoride, and 68Ga-labeled prostate-specific membrane antigen, may also be considered in certain cases, although more data are needed to support their use in surveillance after surgical resection of localized RCC 1.

From the Research

Benefits of PET Scan in Diagnosing Renal Cancer

• PET scans can be beneficial in diagnosing renal cancer, particularly in the metastatic setting and response to therapy 2, 3, 4, 5.
• Functional PET/CT has proven helpful in the diagnosis and management of many cancers, and its value in renal cell carcinoma (RCC) is still evolving 2.
• FDG is probably the most useful radiotracer in RCC, although CAIX imaging can be helpful in clear cell RCC 2.

PET Scan in Evaluating Treatment Response

• PET scans can evaluate early response to treatment by tyrosine kinase inhibitors (TKIs) in advanced RCC 3, 4, 5.
• The degree of reduction in 18F-FDG uptake after sunitinib treatment adds valuable prognostic information 3.
• PET scans can predict progression-free survival (PFS) and overall survival (OS) in patients with advanced RCC treated with TKIs 4, 5.

Limitations of PET Scan in Renal Cancer

• Conventional anatomic imaging is limited, and functional PET/CT has its own limitations in differentiating primary disease from normal parenchyma 2.
• Many innovative radiotracers have been tested in RCC, but robust differentiation of primary disease from normal parenchyma remains elusive for almost all of them 2.
• Excreted FDG present in the urinary tract can mimic metastatic tumor or lymphoma findings and interfere with image reading 6.

Comparison with Other Imaging Modalities

• PET scans can provide additional information compared to CT scans in evaluating treatment response and predicting PFS and OS 3, 4, 5.
• Careful investigation of the renal cortex by FDG PET and review of anatomical images, such as CT and MRI, have important roles in the detection of renal tumor 6.