13 General introduction stage END having additional morbidity for the patient, inefficient use of resources, time, and extra costs as a consequence. Another disadvantage of DOI is that it has been used intermittently with tumor thickness, which is also a predictor of RLNM (28-31). However, the 8th edition of the AJCC addressed this problem by providing a clear definition for DOI (15). Alternatively, some centers perform SLNB to rule out the presence of occult RLNM. Indeed, detection rates of 95% (32-34), 0.93 sensitivity and NPV of 0.88-1 (33-37), make SLNB a reliable method to detect occult RLNM during surgery. Since the success rate of SLNB depends on the experience and technical expertise of the team performing the procedure, its implementation in routine patient care knows difficulties (11). Histopathological evaluation of the primary tumor and RLNM as gold standard Besides TNM staging, the 7th and 8th edition of the AJCC recommend to collect several histopathological characteristics as they can affect clinical decision making (14, 15). Among them are: the maximum macroscopic diameter of a tumor in mm, which should be measured using the resection specimen. However, when the histological extent of the tumor is greater than macroscopically apparent, the maximum diameter should be measured microscopically (38). The DOI in mm (38), which is measured by finding the “horizon” of the basement membrane of adjacent squamous mucosa and drawing a perpendicular “plump line” from the earlier defined horizon to the deepest point of tumor invasion (15). A DOI > 4 mm is significantly associated with – occult – RLNM in early OSCC (26, 27). The histopathological grade (G) of OSCC is called on the degree of resemblance of the tumor cells to those of the normal epithelium (38). Generally, the following categories are used: cannot be assessed (GX), well differentiated (G1), moderately differentiated (G2), poorly differentiated (G3), and undifferentiated (G4) (14). Grading is performed on the most aggressive area of the tumor and poor differentiation is associated with poor outcome, despite the fact that it is highly subjective (38-40). The presence or absence of perineural, lymphovascular, or bone invasion should be recorded, as their presence is associated with tumor recurrence, nodal metastasis, and/or poor survival (38, 41). The worse pattern of invasion (WPOI) at the deep margin of OSCC can be assessed as: broad cohesive sheets of cells (WPOI type 1), broad pushing “fingers” or separate large stellate like tumor islands (WPOI type 2), large invasive tumor islands of > 15 cells (WPOI type 3), small invasive tumor islands of ≤ 15 cells including single cell invasion (WPOI type 4), or tumor satellites of any size ≥ 1 mm away from the main tumor or next closest satellite (20X objective) (WPOI type 5) (42, 43). Seen its signifi1
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