These were the main findings of a new study of more than 300 individuals.
Previous studies have shown an association between widespread disease and loss of SMAD4 immunolabeling, according to the paper. Biomarkers to predict which pancreatic adenocarcinoma patients may benefit from more aggressive therapy are lacking, wrote Emily J. Anstadt, MD, of the University of Pennsylvania, Philadelphia, and colleagues, in their paper published in Cancer.
The human transcription factor and tumor suppressor, mothers against decapentaplegic homolog 4 (SMAD4), “may be a promising biomarker for predicting the likelihood of experiencing distant failure in patients with pancreatic cancer,” the researchers wrote.
“For patients with pancreatic cancer, improving treatments and overall outcomes remains invaluable,” Dr. Anstadt said in an interview. However, the disparate clinical courses make studies of this patient population challenging.
“As with much of medicine and oncology at this time, we feel the key to better outcomes lies in personalizing treatment strategies and relying on tumor genetics to predict tumor behavior and guide us towards individualized optimal treatments,” she added.
Study Methods and Results
The researchers identified 322 patients with resected stage I–III pancreatic adenocarcinoma from The Cancer Genome Atlas (TCGA) and the International Cancer Genome Consortium (ICGC). The study population included 165 patients from the TCGA who served as the training set and 157 patients from the ICGC who served as the validation set.
The primary outcomes were overall survival (OS) and distant metastasis-free survival (DMFS).
A total of 50 patients in the TCGA group (30%) had at least one of the three identified SMAD4 genomic aberrations.
Using the TCGA group, the researchers conducted a regression analysis on the survival outcomes as a function of either the presence of an SMAD4 genomic aberration or the expression of messenger RNA sequencing (RNA-seq). They then used the ICGC to validate whether SMAD4 RNA-seq expression improved risk stratification for OS and DMFS in a separate group of patients.
In the TCGA group, 3-year OS for patients with any SMAD4 aberrations vs no SMAD4 aberrations was 18% vs 36% (hazard ratio, 1.55; P = .048). However, the 3-year DMFS for patients with and without SMAD4 aberrations was 14% vs 23%, a nonsignificant difference (HR, 1.33; P = .19).
In a multivariate analysis, SMAD4 aberrations also were associated with increased risk of stage III disease (HR, 1.89; P = .003). The researchers noted that adjuvant radiotherapy and adjuvant chemotherapy were significantly associated with a decreased risk of death in these patients (HR, 0.53 and HR, 0.28, respectively).
In addition, low SMAD4 RNA-seq expression was associated with worse OS and DMFS, (HR, 1.83 and HR, 1.70, respectively) in the TCGA group.
In the ICGC validation group, increased SMAD4 RNA‐seq expression correlated with improved OS (area under the curve .92) and DMFS (AUC, .84).
Dr. Anstadt said she and her colleagues were not surprised by any of their findings, given earlier research’s suggestions of SMAD4 loss having been associated with poor outcomes for pancreatic cancer.
“Prior studies determined SMAD4 status based on immunohistochemistry and different investigators used different scoring systems,” Dr. Anstadt noted, in an interview. “The results of those studies were conflicting, and consequently SMAD4 has not been adopted clinically as part of the work-up or to aid in treatment decisions.”
“It is essential to find robust, reliable, and cost-effective methods for implementing this in the clinic. As such, we were happy to find that expression of SMAD4 by mRNA sequencing may be that method,” she added.
Not Quite Clinic-Ready
“While we are hopeful that this tool will be a reliable method for use in the clinic, it has yet to be validated in a prospective manner,” Dr. Anstadt said in an interview. “In addition, this study showed that [genetic] expression levels are correlated with worse outcomes and can be of prognostic use; however, we have not directly studied whether expression levels can be predictive of treatment response,” she said.
“Practicing oncologists often have to make difficult decisions in situations where there are no clear answers,” Dr. Anstadt continued. “When considering gray-zone treatment recommendations, we often integrate multiple factors to form an opinion. The reality of cancer medicine is that not all those factors we consider have been validated in prospective studies, but together they produce a picture that is clinically useful. We would submit that SMAD4 status should be one of those factors taken into consideration in forming a comprehensive opinion about suitability for resection or radiotherapy.”
In practice, “if this test is prospectively validated in a future study and will impact clinical decision-making, then this cost will be similar to other genetic tests that have been adopted and have been practice-changing in other oncologic fields,” said Dr. Anstadt. “Being able to individualize treatment can also save overall cost; for instance, predicting which patients would not benefit from local radiation or surgery could decrease use and cost in that population,” she said.
Limitations of the current study included the inability to examine interactions between SMAD4 and radiotherapy because of the sample size and the potential for selection bias, the researchers wrote.
Potential Predictive Value
“A major challenge in the management of patients with pancreatic cancer is the difficulty in predicting which patients will develop metastasis early,” said Jatin Roper, MD, a gastroenterologist at Duke University, Durham, North Carolina, in an interview.
“SMAD4 has previously been evaluated as a prognostic marker in pancreatic cancer, but the association between SMAD4 gene expression, gene mutations, and cancer metastasis has not yet been systematically evaluated in patients, said Dr. Roper, who was not involved in the study.
The new study’s main findings that SMAD4 genomic alterations are associated with worse overall survival, but not distant metastasis-free survival, and that increased SMAD4 expression is associated with improved overall survival and distant metastasis-free survival, suggest that SMAD4 gene expression may be a useful marker in predicting clinical outcomes in pancreatic cancer, Dr. Roper said.
In the future the current study may prompt prospective research to determine a potential association between clinical assessment of SMAD4 gene expression at the time of surgical cancer resection and worse overall survival and distant metastasis-free survival, he said.
The study received no outside funding. Dr. Anstadt and Dr. Roper had no financial conflicts to disclose.