Role of parity and human papillomavirus in cervical cancer: the IARC multicentric case-control study.
BACKGROUND
High parity has long been suspected of being associated with an increased risk of cervical cancer, but previous analyses of this association have not taken the strong effect of human papillomavirus (HPV) into account. To assess the role of reproductive factors in the progression from HPV infection to cancer, we did a pooled analysis including only HPV-positive women.


METHODS
We pooled data from eight case-control studies on invasive cervical carcinoma (ICC) and two on in-situ carcinoma (ISC) from four continents. 1465 patients with squamous-cell ICCs, 211 with ISCs, 124 with adenocarcinomas or adenosquamous ICCs, and 255 control women, all positive for HPV DNA by PCR-based assays, were analysed. We calculated pooled odds ratios by means of unconditional multiple logistic regression models, and adjusted them for sexual and non-sexual confounding factors. The 95% CI were estimated by treating the odds ratio as floating absolute risk.


RESULTS
We found a direct association between the number of full-term pregnancies and squamous-cell cancer risk: the odds ratio for seven full-term pregnancies or more was 3.8 (95% CI 2.7-5.5) compared with nulliparous women, and 2.3 (1.6-3.2) compared with women who had one or two full-term pregnancies. There was no significant association between risk of adenocarcinoma or adenosquamous carcinoma and number of full-term pregnancies.


CONCLUSIONS
High parity increases the risk of squamous-cell carcinoma of the cervix among HPV-positive women. A general decline in parity might therefore partly explain the reduction in cervical cancer recently seen in most countries.
Muñoz
Nubia
N
Unit of Field and Intervention Studies, International Agency for Research on Cancer, 150 Cours Albert Thomas, F-69372, Cédex 08, Lyon, France. munoz@iarc.fr
Franceschi
Silvia
S
Bosetti
Cristina
C
Moreno
Victor
V
Herrero
Rolando
R
Smith
Jennifer S
JS
Shah
Keerti V
KV
Meijer
Chris J L M
CJ
Bosch
F Xavier
FX
D000230:Adenocarcinoma / Q000209:etiology / Q000821:virology; D000328:Adult; D002277:Carcinoma / Q000209:etiology / Q000821:virology; D018196:Carcinoma, Adenosquamous / Q000209:etiology / Q000821:virology; D002294:Carcinoma, Squamous Cell / Q000209:etiology / Q000821:virology; D016022:Case-Control Studies; D004279:DNA, Viral / Q000032:analysis; D005260:Female; D020073:Gravidity; D006801:Humans; D016015:Logistic Models; D008875:Middle Aged; D016017:Odds Ratio; D027383:Papillomaviridae / Q000302:isolation & purification; D030361:Papillomavirus Infections / Q000150:complications*; D010298:Parity; D012307:Risk Factors; D014412:Tumor Virus Infections / Q000150:complications*; D002583:Uterine Cervical Neoplasms / Q000209:etiology* / Q000821:virology
D004279:DNA, Viral