Depth of invasion（DOI） introduced in UICC 8th T classification in tongue carcinoma

—Evaluation of histopathological DOI and clinical DOI in consideration of shrinkage rate of the specimen—

Abstract

To clarify the problem of the new T classification in tongue carcinoma, we reviewed the records of 427 previously untreated tongue cancer patients between 2006 and 2015. In the 7^th edition, there were 224 patients in T1, 152 in T2, 42 in T3, and 9 in T4a. In the 8^th edition, there were 204 patients in T1, 149 in T2, and 74 in T3. The T classification was unchanged in 87.9％, upstaged in 10.0％, and downstaged in 2.1％. According to the 7^th edition, 5-year disease-specific survival was 96.4％ in T1, 93.5％ in T2, 79.2％ in T3, and 46.9％ in T4a. In the 8^th edition, 5-year disease-specific survival was 96.7％ in T1, 94.3％ in T2, and 78.8％ in T3. In addition, the mean shrinkage rate of tissue width during preparation of histopathological specimens was 6.8％. Compared with the clinical DOI, the histopathological DOI corrected 6.8％ of the shrinkage rate of the specimen. Clinical DOI was measured by MRI and US. As a result, the DOI measured by MRI before the biopsy was the closest to the histopathological DOI.