Pap Test screening shown to lower incidence of adenocarcinoma of the cervix
New York, NY
Contrary to common opinion, routine cervical screening can identify early-stage adenocarcinoma and adenosquamous carcinoma of the cervix, according to a large case-control study that used routine records of cervical cytology from UK databases.
"Although there can be no doubt about its effectiveness in preventing squamous cell carcinoma, there is little evidence of any benefit on adenocarcinoma and adenosquamous carcinoma of the cervix, and many authors have concluded that it is ineffective," Dr. Peter Sasieni and co-investigators point out in the International Journal of Cancer for August 1.
They evaluated screening histories for 3305 women, ages 20 to 69 years, with invasive cervical cancer diagnosed since 1990. The cancers included adenocarcinomas (19%), adenosquamous carcinomas (4%), and squamous carcinomas (77%).
For each subject, Dr. Sasieni, at the Wolfson Institute of Preventive Medicine in London, and co-researchers chose an age-matched control from the same group practice, and another from a different practice in the same area. They used these data to estimate the magnitude and duration of the low-risk period following a negative smear, and the degree of protection associated with routine screening.
The odds ratio of developing a stage 1B tumor or worse within 2.5 years of an invasive cervical cancer was 0.23 for adenocarcinoma, 0.09 for squamous carcinoma, and 0.10 for adenosquamous carcinoma. The differences between 2.5 and 3.5 years after a negative smear were even larger, with odds ratios of 0.67 for adenocarcinoma, 0.15 for squamous carcinoma, and 0.20 for adenosquamous tumors.
"It is no surprise that screening is less protective against adenocarcinoma of the cervix," Dr. Sasieni's team points out. "These can occur in the endocervical canal and are less amenable to detection at an early stage by exfoliation cytology."
Still, the researchers maintain that screening has a significant impact on the incidence of adenocarcinoma. They estimate that such tumors can be detected, but it may be harder to do so, and requires a shorter lead time than for squamous cell carcinoma.
By contrast, the impact of screening on adenosquamous carcinoma was nearly the same as the impact on squamous carcinoma. The authors theorize that this similarity between the two types "represents phenotypic drift of lesions that evolve from CIN and only later acquire glandular involvement."
Source:Int J Cancer 2009;125:525-529.
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