Patients diagnosed with thymoma, a rare cancer of the thymus gland, may be able to avoid certain cancer treatments associated with severe adverse events if the results of a new test reveal they are at low risk of metastasis, according to a study published today in the journal PLOS ONE.
The paper, by researchers at the Indiana University School of Medicine, reported results on a gene expression profile test designed to predict whether thymoma will metastasize within 5 years.
“Our studies established and validated a nine-gene signature which predicts the likelihood of metastasis more accurately than traditional staging methods, including Masaoka and extent of surgical resection,” commented Sunil Badve, M.D., FRCPath, professor of pathology and laboratory medicine at Indiana University School of Medicine and lead study author. “Since current guidelines recommend adjuvant radiation and chemotherapy for all resected patients with Stage II/III thymoma tumors, it can lead to undertreatment of patients with aggressive tumors diagnosed at an early stage, and overtreatment of slow-growing tumors diagnosed at a later stage.”
Commented Patrick J. Loehrer Sr., M.D., director of the Indiana University Melvin and Bren Simon Cancer Center in Indianapolis, “The real secret to the management of rare tumors is a better understanding of their biology. This is a first step in having a clinically meaningful tool for thymoma patients.”
Multi-institutional archival primary thymoma tumors were analyzed in a training set (N=36), and subsequently validated in an independent, multi-institutional cohort of patients (N=75). In the training set, 5-year and 10-year metastasis-free survival rates were 77% and 26% for the predicted low risk for metastasis (Class 1) and high risk for metastasis (Class 2), (P=0.0047, log rank), respectively. For the validation set, 5-year metastasis-free survival rates were 97% and 30% for the predicted low risk (Class I) and high risk (Class 2) (P=0.0004, long rank), respectively.
Traditional staging includes use of Masaoka stages and extent of surgical resection. 5-year metastatic-free survival rates for the validation set were 49% and 41% for Masaoka Stages I/II and III/IV (P=0.0537, log rank), respectively. 5-year metastatic-free survival rates for the validation set were 56% and 29% for extent of resection with no evidence of disease and residual disease (P=0.0081, log rank).
Thymoma is a cancer of the thymus, the small organ that is part of the lymph system and located just beneath the breast bone. It is an extremely rare cancer, with only 500 diagnoses annually in the U.S. The cause is unknown and the disease is most often detected during a chest x-ray or CT scan that is being performed for another reason. It seems to affect more women than men, usually between the ages of 40 and 70. Treatment includes surgical removal of the thymus, called a thymectomy, usually followed by chemotherapy and radiation.
The study, titled A Gene Signature to Determine Metastatic Behavior in Thymomas, was published in the July 24, 2013 issue of PLOS ONE and authored by Dr. Badve, Yesim Gökmen-Polar, Ph.D. and Patrick J. Loehrer Sr., M.D., all of Indiana University School of Medicine.
The gene test, called DecisionDx-Thymoma, is currently being made available to physicians by Castle Biosciences, through a license agreement with Indiana University. More information can be found at here.