In Situ Mesothelioma Diagnosis Rare but Possible

Pleural mesothelioma, an unusual form of cancer caused by exposure to airborne asbestos fibers, often has a complex growth pattern resulting in metastasis, leading to the diagnosis of a secondary cancer. Mesothelioma is diffuse and spreads throughout the body by entering the blood stream or the lymphatic system.   It is rare that “in situ” mesothelioma, mesothelioma cells that are confined to the site of origin and have not invaded neighboring tissue through metastasis, is diagnosed in malignant mesothelioma patients.

According to a report in the November, 2005 issue of Archives of Pathology & Laboratory Medicine, in fact, the authors suggest that in situ should only be used when diagnosing benign reactive mesothelial hyperplasia and not diffuse malignant mesothelioma since “invasion is the most reliable criterion for determining that a mesothelial proliferation is malignant.”

They further state, however, that mesothelial cells demonstrate a higher degree of cytologic atypia (atypical cells) in benign reactive processes than when they are malignant, making an accurate diagnosis difficult.

In the 5 years since, however, scientists say that “the existence of an in situ stage of malignant mesothelioma is now accepted,” although it is often referred to as atypical mesothelial proliferation. The authors of a July 18, 2010 article in the International Journal of Surgical Pathology use the case of a 71-year-old man to present evidence of in situ stage of mesothelioma.

Mesothelioma is a very rare and aggressive cancer.  Symptoms may not appear until up to 50 years after initial exposure to asbestos. However, after symptoms become apparent, mesothelioma may rapidly progress to cause life-threatening complications.  Currently there is no known cure for the disease.