In a study reported in the Journal of the National Cancer Institute, Sundström et al found that women co-infected with high-risk and low-risk human papillomavirus (HPV) had reduced risk of squamous cervical cancer (SCC), but not cancer in situ (CIS) compared with women with high-risk HPV infection alone.
The study involved women from Swedish population-based nested case-control studies who had baseline normal smears in cervical screening. A total of 4,659 smears were collected from women who later developed CIS (n = 524) or SCC (n = 378) and individually matched control subjects who remained free of disease during follow-up. All smears were tested for seven low-risk and 16 high-risk HPV types. Median follow-up from first smear to diagnosis of CIS and SCC was 6.4 and 7.8 years, and median time from last smear to diagnosis was approximately 1 and 3 years.
Reduced Risk of SCC
High-risk HPV was found in 49% to 67% of smears before CIS and in 50% to 57% before SCC; only low-risk HPV was found in 1% to 3% of smears; and both high-risk and low-risk HPV were found in 1% to 5%. Compared with women who were infected with high-risk HPV only, women co-infected with low-risk HPV had reduced risk for SCC (relative risk [RR] = 0.2, 95% confidence interval [CI] = 0.04–0.99) but not for CIS (RR = 1.1, 95% CI = 0.4–3.6). Women positive for both high-risk and low-risk HPV had an average of 4.8 additional years until diagnosis of SCC compared with women who had only high-risk HPV (P = .006).
The investigators concluded, “Co-infection with [low-risk] HPV is associated with a lower risk of future invasive disease and longer time to diagnosis than infection with [high-risk] HPV alone. We propose that co-infection with [low-risk] HPV interferes with the rate of progression to invasive cervical cancer.”
Karin Sundström, MD, PhD, of Karolinska Institutet, is the corresponding author for the Journal of the National Cancer Institute article.
The study was supported by the National Cancer Institute.
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