Evaluation of Microscopic Disease in Oral Tongue Cancer Using Whole-Mount Histopathologic Techniques: Implications for the Management of Head-and-Neck Cancers

Purpose To map the distribution of microscopic disease (MD) in head-and-neck cancer by analyzing digital images of whole-mounted serial sections of tongue cancer specimens. Methods and Materials Ten T1–3 oral tongue cancer specimens were evaluated. The specimens were sliced into 3-mm blocks from which one or more 4-μm slides were taken and digitized to create whole-mounted serial sections. Gross tumor and microscopic disease were digitally contoured on each slide. Lines perpendicular to the gross tumor volume (GTV) edge were created at 0.05-mm intervals and the distance between GTV and MD measured. Results Of 88 slides assessed, 44 (50%) had evidence of MD. Of the 63,809 perpendicular lines drawn along the GTV edges, 2320 (3.6%) encountered microscopic disease along their path. The majority of MD abutted the GTV, and only 26.7% was noncontiguous with the GTV edge. The maximum distance from the border was 7.8 mm. Ninety-nine percent of all MD was within 4.75 mm and 95% was within 3.95 mm of the GTV. Conclusion In this study we were able to assess the distribution of MD more accurately than has been possible with routine pathologic techniques. The results indicate that when the GTV is correctly identified, there is very little MD to be found outside this volume. This has implications for the volume of tissue resected at surgery and the volume included in the clinical target volume in conformal radiotherapy planning.