The major problem associated with histological assessment of surgical margins in oral squamous cell carcinoma is shrinkage of the specimen. It has been observed from the limited literature available, that the total shrinkage of OSCC depends on site , stage , age, fixation and method of resection . Site related shrinkage differences are due to different tissue composition. Moreover, the site specific shrinkage in two different studies is not the same. For example, in case of buccal mucosa total shrinkage is 48.8% versus 71.9%; in tongue 32.4% versus 42% , and in buccal mucosa, post resection shrinkage is 38.3% versus 21.2% . This variation in the site specific shrinkage could be due to tumour associated factors present in the specimen. Method of resection also plays a significant role. Cutting diathermy produces minimal shrinkage when compared with the Harmonic scalpel, conventional scalpel and coagulative diathermy. Conventional scalpel results in maximum shrinkage . Thus, it appears that shrinkage depends upon many intrinsic and extrinsic factors which are unpredictable, uncontrollable and are not constant.
Mistry et al. reported shrinkage of 25.6% in T1/T2 tumour versus 9.2% in T3/T4 tumours. It is hypothesized that late stage tumours cause more tumour related destruction of contractile elements and their replacement by non-contractile tumour tissue which leads to less shrinkage . However, the contradictory results were reported by Cheng et al. (T1/T2: 51.48% and T3/T4: 75%). We feel that in any given specimen, shrinkage is different at different locations. Intratumoural site may show less shrinkage as destruction of contractile elements is more. But what matters are the margins of the specimen and their assessment where the tumour tissue is absent or minimal. In these regions, there is no or minimal destruction of contractile elements which leads to significantly more shrinkage than intratumoural region. Such shrinkage difference was reported by Blasdale et al. in basal cell carcinoma of skin (intratumoural: 11% and tumour free margin: 19%). Hence, we strongly feel that there is no relevance whether the tumour is of T1/T2 or T3/T4 stage.
There is lack of consensus on the definition of involved or adequate surgical margin. The most widely accepted definition of a close margin is a width of 5 mm to 1 mm and that of an involved is less than 1 mm (UK guidelines) . But still the need for reassessment and reestablishment of these guidelines has been stressed in the literature. We believe that this lack of consensus is due to inter-laboratory or inter-institutional differences in the percentage of shrinkage that resulted in disparity in defining the surgical margins.
We recommend that these new UK guidelines should be shrinkage based and future studies are needed in this direction. As calculation of shrinkage is very easy, less time consuming and requires minimum instrumentation (ruler or Vernier caliper), it is feasible to calculate shrinkage for each surgical specimen . We also stress that the pathology reports should designate the distance of tumour from the mucosal and deep resection margin to facilitate the establishment of modified shrinkage based guidelines in future.
We suggest that the true margins should be assessed, if required, by intraoperative analysis (e.g.: frozen section or by less invasive optical diagnostics such as microendoscopy, optical coherence tomography or elastic scattering spectroscopy) and interpreted as involved even if they are classified as severe dysplasia or in situ carcinoma. These methods are not routinely applied because of their cost and complexity. Till today, conventional histopathological assessment with UK guidelines are used worldwide and thus the need for the revised shrinkage based UK guidelines is proposed. It will take many years of prospective study; hence present letter is written to realize the need of the hour.