Increasing number of passes beyond 4 does not increase sensitivity of detection of pancreatic malignancy by endoscopic ultrasound–guided fine-needle aspiration

Increasing number of passes beyond 4 does not increase sensitivity of detection of pancreatic malignancy by endoscopic ultrasound–guided fine-needle aspiration.

This is an article written by contribution of many authors published in Clinical gastroenterology and hepatology that is the official clinical practice journal of the American Gastroenterological Association. In which the authors are aimed to define the yield of EUS-FNA responsible for malignancy of pancreatic mass, and to identify factors which are associated with detection of these malignancies.

After the study they found that only 4 passes of EUS-FNA are sufficient to detect malignant pancreatic masses and if the number of passes increases, it did not increase the sensitivity of detection.

your answer is "the 1950's"