PHOENIX, ARIZ. – Even small pancreatic neuroendocrine tumors have the potential for malignancy and need excision or close monitoring, investigators caution.
A retrospective cohort study following outcomes for patients with nonfunctional pancreatic neuroendocrine tumors (PNETs) 2 cm in diameter or less found that in an unadjusted analysis stratified by surgery type, those who did not have surgery had significantly worse overall survival 5 years after diagnosis, although there were no significant survival differences among all surgery types, reported Dr. Lauren Gratian of Duke University, Durham, N.C.
PNETs 2 cm in size or smaller are increasing in incidence in the United States, Dr. Gratian said at the annual Society of Surgical Oncology Cancer Symposium. "This is important, because their malignant potential is uncertain, and optimal surgical management remains unclear."
Neil Osterweil/Frontline Medical News
Dr. Laura Gratian
She pointed to National Comprehensive Cancer Network (NCCN) guidelines, which say that nonfunctional PNETs 2 cm or smaller are candidates for either enucleation or partial pancreatic resection, and that in certain cases, observation may be considered. Specifically, tumors smaller than 1 cm that were discovered incidentally may be candidates for observation, with the decision based on estimated surgical risk, site of the tumor, and patient comorbidities.
To get a better handle on the incidence of nonfunctional PNETs over time, discern their malignant potential, and see what factors are associated with survival, the investigators drew from the American College of Surgeons’ National Cancer Data Base (NCDB) for records on patients diagnosed from 1998 through 2011 with nonfunctional PNETs that met the criteria. Patients with functional PNETs, carcinoids, and/or exocrine tumors were excluded.
Of the 1,854 patients identified, 487 with more than 1 malignant primary, unknown surgical status, or surgery/pancreatectomy not otherwise specified were excluded, leaving a survival cohort of 1,367. Of this group, 368 (27%) had no surgery, 586 (43%) had a partial pancreatic resection, 324 (24%) had a pancreatoduodenectomy (Whipple procedure) with or without a partial gastrectomy, and 89 (6%) underwent total pancreatectomy.
The researchers found that the incidence of small nonfunctional PNETs as a percentage of all PNETs increased significantly over time, from 7% in 1998 to 20% in 2010.
When they grouped tumors by size (5 mm or smaller, more than 5 mm up to 1 cm, and more than 1 cm up to 2 cm), they found that there were no differences in tumor propensity for either distant metastases (11%, 9%, and 13%, respectively) or regional lymph node involvement (34%, 21%, and 29%).
Patients with distant metastases were significantly more likely to have had no surgery (P less than .001), and patients with partial pancreatic sections were significantly more likely than those who had undergone Whipple or total procedures to have positive surgical margins (P = .009).
An unadjusted analysis of 5-year overall survival by surgery type showed no significant differences among patients treated with the various procedures, but significantly worse outcomes for patients who had no surgery vs. any surgery (P less than .01).
There were no significant differences in survival between patients who had some regional lymph nodes examined compared with those who had no nodal dissection.
In a proportional hazards analysis adjusted for demographic and clinical features, factors significantly associated with overall survival were older age at diagnosis, which was associated with a higher risk of death (hazard ratio, 1.04; 95% confidence interval, 1.02-1.06); later year of diagnosis, associated with a lower risk (HR, 0.85; 95% CI, 0.77-0.94); and Whipple procedure, which was associated with an increased risk for death vs. partial pancreatectomy (HR, 1.88; 95% CI, 1.13-3.11).
Dr. Gratian noted that the study was limited by the inclusion of only malignant tumors in the database; potential coding errors; missing data on grade and stage of diseases; and the lack of information on variables such as disease recurrence, mitotic rates, or the Ki67 proliferative index.
The funding source for the study was not disclosed. Dr. Gratian and her coauthors reported having no financial disclosures.