A new study from Japan has shown that the protein mucin 21 (MUC21) can be used to help pathologists (doctors who study disease) distinguish between a mesothelioma diagnosis and adenocarcinoma diagnosis—a type of non-small cell lung cancer that accounts for roughly 40% of lung cancer cases and is a possible mesothelioma misdiagnosis.

However, unlike other proteins that help doctors diagnose mesothelioma when they’re present int he patient, MUC21 will help doctors reach an accurate diagnosis because it’s absent in cases of mesothelioma.

MUC21 Biomarker Helps Distinguish Between Mesothelioma and Adenocarcinoma

Yuichiro Kai and his team wanted to find a negative immunohistochemical marker—that is a protein that does not show up in mesothelioma cases—that pathologists can use to differentiate between adenocarcinoma and mesothelioma.

Through their research, Kai and his team determined that MUC21 shows up in only 3% of epithelioid cases, compared to 96% of the adenocarcinoma cases.

Finding a negative biomarker is essential because at this moment in time there are no biomarkers that allow doctors to diagnose a patient with epithelioid mesothelioma definitively. Not having a diagnosis method prevents patients from receiving the correct treatment in a timely manner if they receive the proper treatment at all. Discovering negative biomarkers like MUC21 brings doctors one step closer to a more accurate mesothelioma diagnosis method.

How Can Mesothelioma Be Mistaken For Another Cancer?

In histology—diagnosing cancer by examining a tumor sample—a pathologist or histologist looks at slivers of cells to examine their nuclei, membranes, cytoplasm and other cells features. The histologist might also look more broadly at clusters of cells to study their color and shape as a group. What they see is called a histologic pattern, and it can be compared with other known patterns to determine what type of cancer a patient has.

However, one of the reasons that mesothelioma is so difficult to diagnose is it presents in many different ways. In fact, even the same mesothelioma cell type, like epithelioid mesothelioma, can have different histologic patterns. This lack of consistency can make it difficult for pathologists to match the pattern from the biopsy they are looking at with other histologic patterns in a database.

This problem is further compounded when the histological patterns from a patient with mesothelioma mimic or look similar to the ones shown by adenocarcinoma. So, without additional diagnostic measures, pathologists occasionally misdiagnose mesothelioma patients as having adenocarcinoma and vice versa.

The Problems Misdiagnosis Cases

In Kai’s previous study, they reviewed the diseases of patients who died from mesothelioma in Japan. Over the course of their research, Kai and his team realized that lung adenocarcinoma was frequently misdiagnosed as mesothelioma. Even though the patients were still being diagnosed with a form of cancer, the fact that they were being diagnosed with the wrong type of cancer is problematic.

The main problem is that while the treatment plans for mesothelioma and adenocarcinoma may include similar aspects, they are not the same. Mesothelioma treatment is designed to be tailored to the individual and their specific type of cancer. The treatment for adenocarcinoma is also individualized because not all treatments work for every individual or every kind of cancer.

If a patient has been misdiagnosed as having a different type of cancer, then the individualized treatment plans cannot effectively combat the tumor the patient does have.

However, now that MUC21 has been presented as a viable negative biological marker for mesothelioma, the number of patients being misdiagnosed as having adenocarcinoma or the other way around will hopefully decrease. This way all of the patients will be able to start their right individualized treatment plans as early as possible.

Because cancers respond best to treatment when it is started early, that will give the patients the best chance of getting the outcome they want.