Research on Epidemiology of GIST Identifies Risk Factors

Using more accurately defined data than previous studies, a team of investigators at the University of California, San Diego School of Medicine has characterized the epidemiology of gastrointestinal stromal tumors (GIST),¹which are soft tissue sarcomas that develop primarily in the wall of the stomach and small intestine.

The goal of this research is to provide clinicians with a better understanding of important risk factors when evaluating patients with GIST. The authors report several findings that are novel or inconsistent with earlier reports, including racial disparities in incidence and survival.

Previous population-based epidemiologic studies on GIST used cancer registry data that were collected before 2001, when GIST-specific histology coding was introduced in medical coding. This resulted in the inclusion of data from patients with non-GIST abdominal or gastrointestinal sarcomas, including leiomyosarcomas, spindle cell, myofibroblastic, desmoid, and KIT-positive metastatic melanomas.

In contrast, lead author Jason K. Sicklick, MD, assistant professor of surgery and a surgical oncologist at UC San Diego Health System, and his colleagues analyzed data in the Surveillance, Epidemiology, and End Results (SEER) database derived from 6142 patients who were diagnosed with GIST after 2001.

“Previous journal articles never clearly differentiated GIST from several other tumors, even though they have different biologies,” noted Sicklick. “This study more clearly identifies at-risk populations in the United States as well as incidence rates, survival trends, and risk factors for the disease.”

The authors found that the incidence of GIST rose over the period in the study from 5.5 cases per 1 million people in 2001 to 7.8 in 2011, and the overall rate was 6.8 cases per 1 million people. The incidence of GIST increased with age, peaking at 30.6 per 1 million people among patients 70 to 79 years of age, and the median age at diagnosis was 64 years. The data also showed that GIST was 1.35 times more common in males than in females. These findings were largely similar to previous studies, although the sex difference in risk had not been previously observed.^2,3

Also consistent with other studies was the finding that the incidence of GIST was lower in Hispanic patients than in non-Hispanic, and that the greatest increase in incidence was observed in blacks, who were twice as likely as whites to develop GIST. The most notable finding, however, was that Asians and Pacific Islanders were at 1.5 times greater risk than whites, a difference that had not been observed in epidemiologic studies using older data.

Clinical Pearls

• This study is the first characterization of GIST epidemiology that does not include confounding data from non-GIST abdominal or gastrointestinal sarcomas.
• Asian/Pacific Islanders have a greater risk of developing GIST than whites (rate ratio = 1.50).
• The reported 5-year overall survival rates were 77% for localized disease at diagnosis, 64% for regional, and 41% for metastatic.
• Contrary to previous studies, black race was associated with decreased overall survival.
• The reasons for racial disparities in incidence and survival are unknown.
• Other independent risk factors for decreased overall survival were older age at diagnosis and male sex.

The 5-year GIST-specific survival rate in this study was 79%, and 5-year overall survival rate was 77% for patients with localized disease at diagnosis—64% for patients with regional disease, 41% for those with metastatic disease. Multivariate analyses identified older age at diagnosis, advanced disease at diagnosis, male sex, and black race as independent risk factors for decreased overall survival, while the same factors were also risk factors for decreased GIST-specific survival in addition to earlier year of diagnosis.

The poorer 5-year survival for blacks in the 2001-2011 data contradicted a previous report using SEER data from 1992-2005.⁴The authors of the previous study had reported that the racial disparities in survival had disappeared because of increased surgical resection rates and decreased perioperative mortality in black patients since 2000. The reason for the continued disparity observed in the new survey is unclear, although it may be related to the exclusion of confounding data unrelated to GIST.

Commenting on the results, Sicklick said, “For the first time, we are characterizing only GIST epidemiology and not the epidemiology of GIST and other gastrointestinal sarcomas. The findings that Asians/Pacific Islanders are at higher risk for GIST is new and important when evaluating these patients. Finally, in contrast to prior reports that suggest that African Americans have similar survival rates as Caucasians, we find this is not the case. This racial disparity may be multifactorial, but the underlying reason is unknown.”

References

1. Ma GL, Murphy JD, Martinez ME, Sicklick JK. Epidemiology of gastrointestinal stromal tumors in the era of histology codes: results of a population-based study [published online ahead of print October 2, 2014].Cancer Epidemiol Biomarkers Prev. pii: cebp.1002.2014.
2. Tran T, Davila JA, El-Serag HB. The epidemiology of malignant gastrointestinal stromal tumors: an analysis of 1,458 cases from 1992 to 2000.Am J Gastroenterol. 2005;100(1):162-168.
3. Perez EA, Livingstone AS, Franceschi D, et al. Current incidence and outcomes of gastrointestinal mesenchymal tumors including gastrointestinal stromal tumors.J Am Coll Surg. 2006;202(4):623-629.
4. Cheung MC, Zhuge Y, Yang R, Koniaris LG. Disappearance of racial disparities in gastrointestinal stromal tumor outcomes.J Am Coll Surg. 2009;209(1):7-16.