Active surveillance for very low-risk papillary thyroid carcinoma: experience and perspectives from Japan
Low-risk papillary thyroid carcinoma (PTC) has been treated using lobectomy in Japan. This represents a very different approach to that used in Western countries, where the majority of patients have been treated with total thyroidectomy followed by radioactive iodine (RAI). Given the excellent survival and lower risk of surgical complications, Western guidelines have recently adopted a limited surgical approach for low-risk PTC. The treatment paradigm has shifted from a one-size-fits-all approach to more individualized protocols under the concept of risk-adapted management and treatment policies in the East and West have become increasingly integrated. The incidence of thyroid cancer has continued increasing around the world, mainly thanks to the increased detection of small PTCs, and debate is now emerging regarding the potential for overdiagnosis and overtreatment of subclinical thyroid cancers. Countermeasures to the phenomenon have been explored. Guidelines have been establishing new standards for cancer screening and clinical diagnosis. Pathologists have proposed changing the diagnostic criteria and terminology for indolent thyroid tumors. Since the 1990s, two Japanese institutions have initiated prospective trials of active surveillance for asymptomatic papillary microcarcinoma (PMC). These trials verified that the vast majority of tumors did not progress during active surveillance and outcomes were unaffected by delaying surgery. The Japanese guidelines adopted active surveillance management for asymptomatic PMC in 2010. The 2015 American Thyroid Association (ATA) guidelines have accepted the policy as an alternative to immediate surgery in patients with very low-risk tumors. Further studies have revealed that PMC was less progressive in older patients than in younger patients. Strong calcification and poor vascularity were indicators of stable disease. Several clinical issues remain unsolved in terms of active surveillance options for very low-risk PTC. Studies on patient-reported outcomes are still lacking and more specific predictors for the progression of low-risk PTC at the time of diagnosis are in demand.