Are thin HSILs of the cervix at risk to invasion?

Background:

Thin high-grade squamous intraepithelial lesions (HSIL) are a variant of HSILs of the cervix that are ≤9 cells thick. These lesions usually develop in early metaplastic squamous epithelium of the transformation zone (TZ) of younger women without anteceding low-grade squamous intraepithelial lesions (LSIL). The risk of thin HSIL to become invasive is unclear.

Material and method:

We studied 32 consecutive cone specimens of patients with micro-invasive sqaumous cell carcinoma of the cervix FIGO stage Ia1.

Results:

Among the 32 patients with micro-invasive squamous cell carcinoma, 30 (94%) cone specimen showed micro-invasion originating from a field of HSIL > 9 cell layers thick. 2 cone specimens (6%) showed micro-invasion originating from a field of HSIL 8 – 10 cells thick.

Conclusion:

Thin HSILs seem to have no significant risk to progress to invasion. We postulate two latency periods in the transition of thin HSLs to early invasive squamous cell cancer. The first latency period is between the manifestation of a thin HSIL and the appearance of a HSIL with more than 9 cell layers after intraepithelial proliferation. The second latency period is between HSIL > 9 cell layers thick and lesions capable of early invasion.