An uncommon form of mesothelioma was the focus of two retrospective studies published this week: one focusing on untested treatments and the other on experimental gene research.

The studies, published one day apart, took aim at peritoneal mesothelioma, an atypical form of the disease that affects the lining of the abdomen rather than the lungs. Peritoneal mesothelioma accounts for roughly 15-20 percent of all mesothelioma cases each year.

The first study, published March 20 in BMC Cancer, concentrated on treatment options if the cancer returns following a standard course of chemotherapy. The team of Japanese researchers from the National Cancer Center Hospital in Tokyo wanted to see whether a second course of chemotherapy would extend patients’ lives.

Owing to the scarcity of peritoneal mesothelioma cases, the team had little information to work with, noting that there is no standard of treatment for the disease and most cases follow the chemo protocols for pleural mesothelioma.

Records Check

After combing through patient records, the team identified 26 peritoneal mesothelioma patients who got a second course of chemo and compared their results to 54 patients who received only an initial course of chemo.

They found that while patient results matched up after initial chemotherapy treatment — with patients in both groups averaging 7.3 months before the cancer returned — those who underwent a second round of chemo typically lived three months longer: 16.9 months versus 16.6 months. This lines up with a cancer recurrence rate of 3.2 months after the second course of treatment.

Interestingly, they also found that patients who received at least six cycles of a specific chemotherapy cocktail — Pemetrexed, which goes by the brand name Altima, in combination with one of several platinum-based drugs — in their first round of chemotherapy tended to live longer after a second course of chemo than those who did not receive the cocktail.

Given these findings, the team concluded that “second-line chemotherapy may be an option for refractory malignant peritoneal mesothelioma, especially in patients who have completed six cycles of platinum plus pemetrexed as first-line chemotherapy.”

Protein Research

The second study, which was published March 19, was more experimental in nature. This retrospective research focused on the link between peritoneal mesothelioma and the protein PD-L1, a molecule that can inhibit the body’s natural immune response.

Some cancers secrete the protein to shield themselves from the body’s natural defenses, leading it and similar proteins to be dubbed “checkpoint” molecules. Researchers from the Rutgers Cancer Institute of New Jersey decided to see whether peritoneal mesothelioma secretes large quantities of PD-L1.

The researchers located tissue samples from 20 patients and determined that nearly 75 percent of the peritoneal tumors they tested “overexpressed” the protein, as determined by multiple scoring systems.

More Proteins, More Problems

They also found that patients with tumors secreting the highest levels of PD-L1 didn’t live as long as those whose tumors did not produce the protein: an overall survival time of four years versus more than nine years.

According to the researchers, this finding could give oncologists a new avenue to fight peritoneal mesothelioma: a class of drugs known as immune checkpoint inhibitors, which can disrupt PD-L1’s ability to block the immune response.

“We are excited for checkpoint inhibition to be an effective treatment option for patients with this rare cancer,” the team reported. “Our plan will be to test checkpoint inhibition in patients prospectively to determine whether or not it is associated with significant anti-tumor activity.”

The group’s findings were presented at the Society of Surgical Oncology’s International Conference on Surgical Cancer Care.

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