Adding a Certain Immunotherapy Drug to Chemotherapy May Benefit Patients With Thymoma, a Type of Rare Cancer

Patients with thymic carcinoma or type B3 thymoma — a rare cancer that attacks a person’s thymus — whose disease has progressed after chemotherapy may have a new standard treatment option, according to the authors of a study recently published in The Lancet Oncology.

Findings from the phase 2 CAVEATT trial demonstrated that the addition of Bavencio (avelumab) to the chemotherapy Inlyta (axitinib) benefitted this patient population.

The thymus, according to information from Memorial Sloan Kettering Cancer Center in New York, is a small organ found underneath a person’s breastbone. Thymic tumors are extremely rare. In fact, the cancer is diagnosed in approximately 500 people in the United States each year, according to Memorial Sloan Kettering Cancer Center.

Results from the single-institution study showed that 11 of the 32 patients enrolled onto the trial derived a response from the combination of Bavencio and Inlyta. However, none of those patients with the rare cancer achieved a complete response — which is the disappearance of all sings of the cancer.

Moreover, the data indicated that the disease control rate — which is often defined as the percentage of patients whose disease shrinks or remains stable over a period of time — was 91%. Sixty-six percent of the patients also had a reduction in the size of their tumor(s) from enrollment.

Four of the 32 patients had to discontinue treatment because of side effects and one because of the development of a blood cancer. Most of the patients, according to the findings, indicated that the side effects were mild to moderate in terms of severity.

Expressing Concern

One expert, who was not involved in the study, expressed their concerns and noted that the combination of Bavencio and Inlyta may not be suitable to treat most thymomas.

“This (study) is really on a treatment that's best for patients with thymic carcinoma,” Dr. Heather Wakelee, a medical oncologist and thoracic specialist at Stanford Health Care in California, said in an interview with CURE®. “They (had) a very small number of thymoma patients, (and) I think that's problematic. Most of us are very, very cautious about using any immune therapy on patients with thymoma. In this study, they kind of de-emphasize toxicity, but there are several (incidences) where the toxicity was very high, very severe for patients with thymoma.”

While the study authors noted that the results are promising for patients with thymic carcinoma, Wakelee was cautious about how the information was presented as well as the inclusion of any thymoma cases in the study at all.

And although certain side effects were low, one of the five patients with thymoma enrolled onto the trial developed polymyositis, a disease that causes the muscles to break down and weaken. She also discussed concerns about administering Bavencio to future patients with thymoma.

“Thymoma is associated with autoimmune disease,” she explained. “If we give immune checkpoint inhibitors to patients with thymoma, their rates of autoimmune complications (are) very, very high. In one of the earliest trials with (Keytruda) that enrolled more thymoma patients, five of the seven patients had severe autoimmune toxicity. And so they had to stop that (treatment group) and most of the other (immune checkpoint inhibitor) trials have moved forward without that. This trial had these very small number of patients and they talk about ‘oh, thymomas, it’s OK.’ But I get really nervous when I hear about that.”

Seek Out Specialist Care

Both thymoma and thymic carcinoma are rare cancers affecting the thymus. However, thymoma cells look like normal thymus cells, grow very slowly and are often localized to the thymus. A thymic carcinoma has cells that are clearly different from thymic cells, grow very quickly and spread easily around the body.

While both diseases are very rare, thymic carcinomas are less common. Wakelee emphasized the importance of seeing someone who specializes in the treatment of thymic malignancies, as “most oncologists in the community will see one or two ever.”

Wakelee also urged patients to collect multiple opinions and “really weigh the risks and benefits of every treatment.”

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