High-grade cervical abnormalities and cervical cancer in women following a negative Pap smear with and without an endocervical component: a cohort study with 10 years of follow-up.

The proportion of Pap smears containing an endocervical component (ECC) has been declining in Australia. Given that ECC negative (ECC-) smears may be associated with reduced sensitivity, we undertook a retrospective cohort study to estimate rates of histologically confirmed high-grade cervical abnormality (HGA) and cancer in women with negative Pap smears with and without an ECC. Women 18-69 years with at least two Pap smears between 1 January 2001 and 31 December 2010 with the first smear in that period (index smear) showing no abnormality were eligible. Follow-up ended at date of the first abnormal smear, date of histological diagnosis, date of hysterectomy, date of death, or 31 December 2010, whichever came first. ECC status was treated as a time varying exposure. Follow-up was split at each smear after the index smear. Poisson regression was used to estimate adjusted incidence rates and incidence rate ratios (IRR) by ECC status. The incidence rate of histologically confirmed HGA was significantly lower following ECC- smears than after ECC+ smears (adjusted IRR: 0.69, 95%Confidence Interval (CI) 0.62-0.77), particularly at older ages (interaction between ECC status and age, p = 0.001). In contrast, the overall rate of invasive cancer was not significantly different after ECC- than after ECC+ smears (IRR: 1.27, 95%CI 0.90-1.77). In conclusion, women had a lower rate of confirmed HGA and no significant increase in the rate of invasive cervical cancer following ECC- smears. This study does not support differential (accelerated) follow-up in women with a negative smear without an endocervical component.