What Is CAIX?
CAIX (carbonic anhydrase IX) is an enzyme that is expressed at high levels on the surface of many clear cell renal cell carcinoma (ccRCC) cells, the most common type of kidney cancer. In normal tissue, CAIX expression is limited, which makes it an attractive target for both imaging and therapy.
The connection between CAIX and kidney cancer has been well studied. Clear cell RCC often develops in an environment of low oxygen (hypoxia), and CAIX plays a role in helping cancer cells survive under these conditions. The high and relatively specific expression of CAIX in ccRCC opens the door for targeted approaches.
CAIX PET CT Imaging
A CAIX PET CT scan uses a radioactive tracer designed to bind to the CAIX protein. When the tracer is injected and a PET CT scan is performed, areas of CAIX expression light up on the images. This can help identify kidney cancer lesions and their metastatic spread with high specificity for the ccRCC subtype.
CAIX PET CT may be particularly useful in situations where conventional imaging leaves questions unanswered, such as characterising renal masses, detecting recurrence after surgery, or identifying metastatic sites that are difficult to see on standard CT or MRI. It can also help determine whether a patient’s cancer expresses enough CAIX to be a candidate for targeted therapy.
CAIX-Targeted Radioligand Therapy
Following the theranostic model used in prostate cancer (PSMA) and neuroendocrine tumours (DOTATATE), researchers are developing CAIX-targeted radioligand therapy. The principle is the same: if the diagnostic scan confirms CAIX expression, a therapeutic molecule carrying a radiation-delivering isotope can be administered to target those cells.
This approach is still in the early stages of clinical development. While initial research is promising, CAIX-targeted radioligand therapy is not yet a standard treatment. Patients interested in this approach should discuss with their oncologist whether clinical trials or early access programmes are available.
Why This Matters for Kidney Cancer Patients
Kidney cancer treatment has advanced significantly in recent years with the introduction of targeted therapies and immunotherapies. However, not all patients respond to these treatments, and some develop resistance over time. CAIX-targeted theranostics represents a potential additional option that works through a different mechanism: delivering radiation directly to cancer cells carrying the CAIX marker.
The combination of imaging and therapy through the same molecular target means that patient selection can be guided by the diagnostic scan, potentially improving the likelihood that the therapy will reach the intended cells.
Discuss with Your Doctor
If you have been diagnosed with clear cell renal cell carcinoma, ask your oncologist about the role of CAIX imaging and whether targeted approaches could be relevant to your treatment plan. These are evolving areas of nuclear medicine, and availability may vary between centres.