What is RET?

Reviewed by Pathologists
December 28, 2025

RET is a gene that provides instructions for making a protein involved in cell growth and development. The RET protein acts as a receptor on the surface of specific cells, where it receives signals that help control how cells grow, divide, and survive.

RET is considered a biomarker. A biomarker is a measurable feature in a tumour, such as a gene change or protein abnormality, that provides essential information about the cancer and can help guide treatment decisions.

What is the function of RET in normal cells?

In normal cells, the RET protein plays an essential role during early development and in the function of specific nerve and hormone-producing cells.

When specific signals bind to the RET receptor, it activates pathways inside the cell that support normal growth and survival. These signals are tightly controlled, allowing cells to respond appropriately and preventing excessive growth.

What types of cancer are associated with RET?

Changes involving the RET gene are seen in several types of cancer, including:

RET changes can occur in different ways, depending on the cancer type.

How does RET cause cancer?

RET can contribute to cancer when it becomes abnormally activated.

This can happen through:

  • RET mutations, which change the DNA instructions and cause the RET protein to stay active.

  • RET fusions, where part of the RET gene becomes joined to another gene, creating an abnormal protein that sends constant growth signals.

When RET is continuously active, cells receive ongoing signals to grow and divide, even when they should not. Over time, this uncontrolled signaling can lead to tumour formation.

Some RET changes are acquired, meaning they develop only in tumour cells. Others, particularly in medullary thyroid carcinoma, can be inherited, meaning they are present in all cells of the body.

Why do pathologists test for RET?

RET is tested because it is an important predictive biomarker. This means the test result helps predict whether specific treatments are likely to work.

Targeted therapies have been developed to block abnormal RET signaling specifically. These treatments are most effective when a RET mutation or RET fusion is present. If no RET abnormality is found, these treatments are unlikely to help, and other options may be recommended instead.

RET testing also helps clarify the type of cancer and, in some cases, whether genetic counselling should be considered.

How do pathologists test for RET?

RET testing is usually performed on tumour tissue obtained from a biopsy or surgery. In some situations, testing may also be done on a blood sample, known as a liquid biopsy, to detect tumour DNA circulating in the bloodstream.

Common testing methods include:

The choice of test depends on the cancer type and the clinical situation.

How do RET results appear in a pathology report?

RET results are usually found in a section of the pathology report called molecular testing, biomarker testing, or ancillary studies.

Results are commonly reported as:

  • RET mutation detected, followed by the specific mutation.

  • RET fusion detected, with the name of the fusion partner.

  • No RET alteration detected.

Your report may also include a short comment explaining whether the RET result is relevant for targeted therapy or whether further genetic evaluation should be considered.

Questions to ask your doctor

  • Was my tumour tested for RET?

  • Was a RET mutation or RET fusion found?

  • How do my RET results affect my treatment options?

  • Do my RET results suggest inherited risk or the need for genetic counselling?

  • Are there other biomarkers that should be tested?

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