Aim: To evaluate the association between histological grade and depth of invasion in OSCC and to analyse its distribution with respect to gender, tumour site, and tobacco-related habits.

Materials and Methods: This retrospective study included 50 cases of histopathologically confirmed OSCC diagnosed between January 2023 and January 2025. The specimens consisted of 40 biopsies and 10 resection specimens received in the Department of Pathology, KVG Medical College and Hospital, Sullia. Tumours were graded according to the WHO classification into well-differentiated (9 cases), moderately differentiated (38 cases), and poorly differentiated carcinomas (3 cases). Depth of invasion was assessed according to AJCC 8th edition criteria and categorized into ≤5 mm, 6–10 mm, and >10 mm. Statistical analysis was performed using Fisher’s exact test.

Results: Among the 50 cases studied, males constituted the majority with 39 cases (78%), while females accounted for 11 cases (22%). Buccal mucosa was the most common tumour site, observed in 26 cases (52%), followed by tongue in 13 cases (26%), lip in 6 cases (12%), and other sites in 5 cases (10%). A history of tobacco use was noted in 36 patients (72%).
Histologically, moderately differentiated OSCC was the most frequent subtype, accounting for 38 cases (76%), followed by well-differentiated carcinoma in 9 cases (18%) and poorly differentiated carcinoma in 3 cases (6%).

Regarding depth of invasion, 19 cases (38%) showed DOI ≤5 mm, 18 cases (36%) had DOI between 6–10 mm, and 13 cases (26%) demonstrated DOI >10 mm. A significant correlation was observed between histological grade and depth of invasion. All well-differentiated tumours showed DOI ≤5 mm, whereas poorly differentiated tumours consistently demonstrated deeper invasion (>10 mm). Fisher’s exact test revealed a statistically significant association between higher histological grade and increased DOI (p < 0.05).