Study Determines Association of Gallbladder Polyps and Gallbladder Cancer

A study published in JAMA Network Open called into question the current strategy of monitoring polyps to proactively detect a gallbladder cancer. 

The study results indicated that the natural history of gallbladder polyps is to grow over time. Polyps less than 10 mm in size were rarely correlated with gallbladder cancer, and even those sized 10 mm or larger rarely did. Overall, gallbladder cancer rates in the study were found to be low and similar among both patients with and without gallbladder polyps.

“Our study suggests that growth over time is the natural history of (gallbladder polyps) and that even stability for 5 years does not guarantee subsequent stability,” the authors wrote. “Furthermore, we did not find evidence that this subsequent growth was associated with (gallbladder cancer).” 

This cohort study evaluated 622,227 adult members of Kaiser Permanente Northern California, an integrated healthcare delivery system, enrolled between January 1, 1995, and December 31, 2014. The gallbladder cancer cohort comprised a total of 365 adults with gallbladder cancer and prior ultrasonography, and the gallbladder polyps cohort comprised 35,856 adults with gallbladder polyps present on ultrasonography. 

Ultimately, gallbladder polyps were found in 22 patients (6.0%) in the gallbladder cancer cohort and in 35,870 of 622,227 adults (5.8%) who underwent abdominal ultrasonography. Of these individuals, 19 (0.053%) were diagnosed with gallbladder cancer, similar to those without gallbladder polyps (316 of 586,357 [0.054%]). Moreover, the unadjusted gallbladder cancer rate per 100,000 person-years was 11.3 (95% CI, 6.2-16.3) overall and increased with polyp size, from 1.3 (95% CI, 0-4.0) with initial size of less than 6 mm (n = 17,531) to 128.2 (95% CI, 39.4-217.0) with initial size of 10 mm or larger (n = 2,055). 

Of those who were observed for at least 1 year, the rate was 3.6 (95% CI, 0.7-6.5) per 100,000 person-years. Even further, in 6,359 patients with evaluable follow-up, unadjusted cumulative probabilities of polyp growth of at least 2 mm at 10 years were 66.2% (95% CI, 62.3%-70.0%) in polyps initially less than 6 mm and 52.9% (95% CI, 47.1%-59.0%) in polyps initially 6 mm to less than 10 mm.

“Our findings call into question the European societies’ recommendations for follow-up of GP,” the authors wrote. “Those call for follow-up at 1, 3, and 5 years for polyps smaller than 6 mm and at 6 months and yearly for 5 years for polyps sized between 6 mm and 9 mm.” 

According to the researchers, cholecystectomy is recommended for polyps sized 10 mm or larger and for polyps that grow at least 2 mm.

“Our findings do support the position of the American College of Radiology that polyps smaller than 7 mm do not need follow-up and suggest that this may also apply to polyps sized between 7 mm and less than 10 mm,” the authors continued. “Further studies are needed to validate this approach.” 

It was suggested that a limited strategy of 1 or 2 follow-up ultrasonography in the subsequent year or 2 years should provide adequate reassurance, if necessary. Otherwise, researchers indicated that the number of yearly ultrasonography needed to detect gallbladder cancer would be enormous. 

The researchers indicated that their study also raises questions for further studies to confirm and analyze the risk factors for growth in gallbladder polyps. Whether the slower growth of larger polyps is real or a product of measurement is not yet clear. Furthermore, if studies confirm that Charlson Comorbidity Index score is in actuality associated with more growth, the mechanisms have yet to be elucidated. 

“Further studies are needed to address the utility of a higher size threshold to recommend cholecystectomy as well as the practicality and usefulness of determining whether (gallbladder polyps) are adenomatous,” the authors wrote. 

Reference:

Szpakowski J, Tucker L. Outcomes of Gallbladder Polyps and Their Association With Gallbladder Cancer in a 20-Year Cohort. JAMA Network Open. doi:10.1001/jamanetworkopen.2020.5143.