Human Papillomavirus Testing and Size of CIN3: Implications for the Risk of Microinvasive Cervical Carcinoma

(1) Background/Objectives: Human papillomavirus (HPV) testing is hypothesised to detect cervical intraepithelial neoplasia grade 3 (CIN3) earlier than cervical cytology, which could translate into several clinical benefits. This study aimed to confirm that HPV testing detects CIN3 lesions of smaller size (or linear extension) and to assess whether this is associated with a decreased risk of stromal microinvasion (≤3 mm) (microinvasive or stage IA1 cervical carcinoma). (2) Methods: The study was conducted in a referral centre for cervical pathology in Italy. Eligible were 3744 patients aged 30-64 years who underwent local excision of the cervix between 1992 and 2021 and were diagnosed with CIN3, with or without microinvasion. Data were analysed using logistic and multinomial regression models. (3) Results: Overall, 1156 (30.9%) CIN3 cases were detected by the HPV test, and 2588 (69.1%) by cervical cytology. The lesion size was smaller in HPV test-detected CIN3 (median, 6 mm; interquartile range (IQR), 4-8 mm) than in cytology-detected CIN3 (median, 7 mm; IQR, 5-9 mm; p < 0.001). HPV test-detected CIN3 was over 50% less likely to have a size >6 mm combined with massive glandular crypt involvement. Stromal microinvasion occurred in 20/1156 (1.7%) HPV test-detected lesions versus 87/2588 (3.4%) cytology-detected lesions (p = 0.006), corresponding to an approximately 50% lower age-adjusted risk. The smaller size of HPV test-detected CIN3 and its lower degree of glandular crypt involvement interacted additively, rather than multiplicatively, in reducing the risk of stromal microinvasion. Over 46% of the association between detection mode and stromal microinvasion was explained by the size/involvement composite variable. (4) Conclusions: HPV testing detects CIN3 lesions of smaller size than cervical cytology. HPV test-detected CIN3 has a lower risk of stromal microinvasion. This association is mediated to a substantial extent by the smaller lesion size and the less extensive glandular crypt involvement, which interact in an additive manner. These findings may have other important clinical implications. First, the prevalence of disease persistence after treatment may decrease. Second, smaller lesions are likely to be treated with more limited excisions. Third, this may contribute to a lower rate of preterm birth in subsequent pregnancies.