Introduction/Background A stromal invasion depth is a basic prognostic parameter in vulvar carcinoma as it is used to determine IA and IB substages, that have different management. A standard technique to measure the depth of invasion is described in the 8th ed. of TNM Classification of Malignant Tumours, and defined as the distance from the adjacent most superficial dermal papilla to the deepest point of invasion. As an alternative technique in FIGO (2021) staging, it was proposed to measure the depth not from a dermal papilla, but from the deepest, adjacent rete ridge (or nearest dysplastic rete peg). The purpose of this study is to compare both techniques and to assess the likelihood of re-staging after applying the alternative method proposed by FIGO.

Methodology A total of 20 cases of stage I vulvar cancer were included in the study. All patients underwent surgical treatment in 2020–2021 at NN Alexandrov National Cancer Centre of Belarus. A retrospective assessment of stromal invasion using both methods was performed by a single pathologist specialized in gynecological oncology. Analysis of the normality of data distribution was carried out on the basis of the Shapiro-Wilk’s W test. The Mann-Whitney U-test was used to compare two independent samples. The Bland-Altman analysis was used to compare the two measurement methods.

Results The depth of tumor invasion by the standard and alternative methods was 2.8 (0.95; 9.5) and 2.45 (0.3; 8.95) mm respectively (p<0,05). However, despite significant differences, restaging occurred in only one case (IB to IA – 2.0 mm to 0.9 mm), which corresponds to 5% probability.

Conclusion The study revealed significant differences in the measurement using standard and alternative methods, which with a probability of 5%, can lead to tumor downstaging. Prospective randomized trials with a large number of patients and survival analyzes are needed.