[1149] The Clinical Significance of “Squamous Intraepithelial Lesion (SIL) of Indeterminate Grade” as a Distinct Cytologic Category.

Dorothy Wong, Crystal Teschendorf, Grace Y Lin, Farnaz Hasteh. University of CA, San Diego

Background: "Squamous intraepithelial lesion of indeterminate grade" (SIL) was introduced in the 2001 Bethesda System for cervical lesions that lie between low-grade or high-grade lesions without discussion of follow-up or its clinical significance. At our institution we use the SIL terminology for such borderline lesions, which is similar to “low grade squamous intraepithelial lesion cannot exclude high-grade squamous intraepithelial lesion (LSIL-H)” utilized by some studies. In this study, we evaluated the follow-up of these borderline lesions collected over a 3 year period and compared them to the follow-up results of low-grade or high-grade squamous intraepithelial lesions (LSIL or HSIL) on Pap smears.
Design: A computer-generated review of cervical pap smears (100% Surepath) diagnosed as SIL from 01/2007 through 01/2010 revealed 152 cases. Histologic outcomes (cervical biopsy, endocervical curettage, loop electrosurgical excision procedure) or follow-up pap smears with available high-risk HPV serologies were obtained for 127 (84%) of these cases. Control groups of 150 cases with a Pap smear diagnosis of LSIL or HSIL with histologic follow-up were selected sequentially from this same time period. Patients with <6 months follow-up and no follow-up were excluded. If multiple follow-up specimens were available the highest degree of dysplasia was used.
Results: On follow-up, HSIL (cervical intraepithelial neoplasia (CIN) grade 2 or 3) was identified in 21% (27/127) of SIL cases, 8.7% (13/150) of LSIL cases and 69% (104/150) of HSIL cases. LSIL (CIN 1) was identified in 30.7% (39/127) of SIL cases, 59% (89/150) of LSIL cases and 17% (26/150) of HSIL cases. ASC-US (atypical squamous cells of undetermined significance) was identified in 20.5% (26/127) of SIL cases with most positive for high-risk HPV at 61.5% (16/26). In comparison, the ASC-US rate was similar for both the LSIL and HSIL control groups (7.3% and 6.7% respectively). A diagnosis of benign was identified in 27.6% (35/127) of SIL cases, 24.7% (37/150) of LSIL cases, but only 6.7% (10/150) of HSIL cases. The histologic outcomes between the SIL, LSIL and HSIL groups are statistically different (p<0.001).
Conclusions: The results showed that patients with the cytologic diagnosis of “SIL of indeterminate grade” have histologic outcomes which are intermediate between and statistically significantly different from patients with either a LSIL or HSIL diagnosis. Our findings support prior studies evaluating the follow-up of patients with LSIL-H and support retaining SIL as a unique category in the Bethesda system.
Category: Gynecologic & Obstetrics

Monday, February 28, 2011 9:30 AM

Poster Session I Stowell-Orbison/Surgical Pathology/Autopsy Awards Poster Session # 127, Monday Morning


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