Annemarie Shepherd, MD, medical director of Fred Hutch Cancer Center – Proton Therapy, has a special interest in thymic cancers, a type of thoracic cancer. Thoracic cancers develops in the chest, or thoracic cavity, which contains the heart, lungs, esophagus, and other organs.

Shepherd serves on multiple committees in the International Thymic Malignancy Interest Group (ITMIG) and chairs the ITMIG International Tumor Board.

Thymic cancers are extremely rare. They arise from the thymus gland, which is located in the chest above the heart. The thymus gland creates T cells and other immune-related cells that fight infection and is an important immune organ.

There are two major types of thymic tumors — thymomas and thymic carcinomas.

Thymomas are less aggressive than thymic carcinoma and both are less aggressive than lung cancer, which is the most common type of thoracic cancer. Thymomas are very slow growing and tend to appear in younger populations. The average patient age is around 50, but Fred Hutch physicians often see patients in their mid-20s or 30s.

Because the tumor can sometimes secrete antibodies, thymoma is often closely associated with certain autoimmune conditions, especially myasthenia gravis.

When a person is diagnosed with thymic cancer, the first intervention is usually surgery. If the pathology of the tumor shows that the patient’s chance of a recurrence is high, or if the cancer has invaded other parts of the body, such as the lung or the pleura (the lining around the lungs) then patients often receive radiation.

“Patients with thymomas tend to have a good prognosis and many decades to live,” said Shepherd. That is why she believes proton therapy is an especially important treatment option for thymic cancers.

“Because of the potential for patients to continue to live a long life after treatment, sparing the heart from radiation and thereby reducing the risk of cardiovascular problems such as coronary artery disease in the future is so important,” said Shepherd. “The thymus gland lies right above the heart, so in order to know if a patient will benefit from protons, we look at how close the tumor is to the heart before surgery. If all of it lies above the heart, great outcomes can be achieved with standard radiation, but if the tumor has started to wrap around the heart, then proton therapy is preferentially indicated.”

As a particle beam with zero exit dose and minimal delivery of radiation prior to the tumor, proton therapy can more precisely target all its radiation specifically at the tumor. Proton therapy can also be beneficial if there is a larger treatment field, meaning more of the body that must receive radiation, or the tumor is more complicated.

With an existing interest in thoracic cancers, Shepherd is drawn to thymic cancers in part because there is still much controversy and debate over when radiation is indicated in treatment. This controversy fueled her desire to become an expert in finding the best approach for the best outcome.

“At the New York Proton Therapy Center, I began a clinical trial that looked at the benefits versus risks of irradiating the entire pleura with protons to prevent recurrence in patients whose thymic tumor has spread to the pleura,” said Shepherd. “The aim is to decrease the risk of future pleural recurrences, as multiple pleural recurrences are common in thymic tumors. The aim of the trial is to understand if this treatment is worth the potential side effects of scarring or pneumonitis.”

The trial is still ongoing.

Shepherd also became interested in thymic cancers because of the young, motivated patient population and the fact it’s a rare cancer, which means it doesn’t receive as much funding for research. Shepherd wants to be an advocate.

“I want to get the word out about proton therapy to the thymoma community,” she said. “I hope it will help patients to find the best care, even if there isn’t a proton therapy center near them.”

This article was originally published December 30, 2024, by Fred Hutch News Service. It is republished with permission.