Hormonal contraception and CIN
Of the 458 subjects in the analysis who were oncogenic HPV-positive at colposcopy-biopsy, 377 (83%) were also oncogenic HPV-positive at screening and of these, 345 (92%) were positive for the same type. At colposcopy-biopsy, HPV16 was detected in specimens from 43 (28%) of the women with negative histology, 27 (20%) of the women with CIN1, and 90 (52%) of the women with ≥CIN2-3. CIN cases were more likely than controls to have two or more oncogenic HPV types detected at colposcopy-biopsy and to have the same type detected at both visits (). Cases were slightly less likely to have undergone cytologic screening prior to study enrollment. Among those previously screened, ≥CIN2-3 cases were more likely to have a history of an abnormal cytologic result.
Distribution of demographic, gynecological, sexual behavior, and HPV characteristics for oncogenic HPV DNA positive women with negative, CIN1, and ≥CIN2-3 histology.
Recent use of DMPA for ≥2 years was inversely associated with ≥CIN2-3, although this association was not significant (adjusted odds ratio (ORadj)=0.5;95% confidence interval (CI)=0.2–1.4) (). Recent use of DMPA for ≥2 years was also inversely associated with CIN1 (ORadj=0.1;95% CI=0.01–0.6). However, there was only one woman with CIN1 with this exposure. When both of the recent DMPA use categories were combined, recent use remained inversely associated with CIN1 (ORadj=0.5;95% CI=0.2–1.0;p=0.04). Recent use of a COC for ≥2 years was not associated with ≥CIN2-3 (ORadj=0.9;95% CI=0.4–1.9) or with CIN1 (ORadj=1.1;95% CI=0.5–2.6). When women who had used COCs for ≥5 years were compared to never users, there was no association with ≥CIN2-3 (ORadj=1.0;95% CI=0.4–2.6) or with CIN1 (ORadj=1.1;95% CI=0.4–3.2). Recent use of a ≥35 mcg of estrogen COC for ≥2 years was not associated with ≥CIN2-3 (ORadj=1.1;95% CI=0.5–2.7). The main analysis was repeated separating women with CIN3 from women with CIN2. The estimates for CIN3 were not significantly (all p>0.13) different from those for CIN2 (data not shown). Likewise, when the main analysis was restricted to HPV16-positive women, results were similar (data not shown).
Odds ratios (OR) and 95% confidence intervals (CI) for the associations between hormonal contraception and CIN among oncogenic HPV DNA positive women.
Hormonal contraception and oncogenic HPV
Oncogenic HPV-positive women were younger and more likely to be nulliparous than HPV-negative women (data not shown). Among histologically-negative women, recent use of DMPA for ≥1 year was significantly associated with oncogenic HPV detection (ORadj=4.7;95% CI=1.4–15.8), but recent COC use was not (). When cases were restricted to HPV16-positive women, the OR for recent DMPA use for ≥1 year increased slightly (ORadj=5.5;95% CI=0.9–34.5).
Odds ratios (OR) and 95% confidence intervals (CI) for the associations between hormonal contraception and oncogenic HPV DNA positivity.
To further explore the association of DMPA use with oncogenic HPV, two additional analyses were performed. First, among 142 histologically-negative women who were HPV-negative at screening, DMPA use for ≥1 year was associated with being oncogenic HPV-positive at colposcopy-biopsy (ORadj=7.3;95% CI=1.5–35.5). Adjusting for the number of new male partners since screening did not change the estimate to an important degree. Second, among 163 histologically-negative women who were oncogenic HPV-positive at screening and did not have any new male partners between visits (women most likely not acquiring a new HPV infection), DMPA use for ≥1 year was not associated with being positive for the same oncogenic HPV type at colposcopy-biopsy (ORadj=1.1;95% CI=0.3–3.7).
Among women with oncogenic HPV, those with CIN were slightly less likely than women with negative histology to report ever use of DMPA in the previous year (borderline statistical significance for ≥CIN2-3). COC use was not associated with ≥CIN2-3 or with CIN1. Recent use of DMPA for ≥1 year was positively associated with detection of oncogenic HPV. The association was attenuated, but remained elevated when women with CIN were included as cases indicating that the association was likely not solely due to difficulty with lesion detection. This relationship did not appear to be due to HPV persistence as measured by type-specific repeat oncogenic HPV positivity, however, DMPA was associated with new HPV infection. COC use was not associated with oncogenic HPV detection.
One study that specifically addressed the risk of cervical cancer associated with DMPA among oncogenic HPV-positive women found no association,16
but Castle et al. found a small increased risk of CIN2 and CIN3 with current injectable contraceptive use.8
This is in contrast to our findings of an inverse association between DMPA use and both CIN1 and ≥CIN2-3 among oncogenic HPV-positive women. Unlike our study, neither of these previous studies used a control group free of cervical disease, which would lead to associations that are spuriously weakened.
Several recent studies,1–3, 17–21
but not all,16
among HPV-positive women have found an increased risk of cervical neoplasia for longer durations (≥10 years) of OC use. We did not find a positive association between ≥2 or ≥5 years of COC use and cervical neoplasia, though the estimates from recent meta-analyses by Smith et al.1
(medium-duration use OR=1.3) and Appleby et al.2
(≥5 years of use risk ratio=1.45) are well inside our confidence interval. However, these results were largely driven by studies conducted outside of the US and subjects likely used very different hormonal contraceptive formulations than those used by women in the US in recent years. Previous studies among HPV-positive women conducted in the US and other industrialized countries did not find an association.3, 17, 18, 21
We found no association between COC use and HPV detection, which is similar to other studies.3, 6, 9
There are a number of mechanisms through which use of hormonal contraceptives might affect the development of HPV infection and risk of cervical neoplasia. First, hormones may inhibit the immune response to HPV infection.22, 23
Our findings that HPV persistence and ≥CIN2-3 were not positively associated with DMPA or COC use do not support this mechanism, however, the interactions between HPV, hormones, and the immune system are not completely understood.
Second, HPV gene expression and cellular proliferation is increased by estrogen and progestin in vitro
Our preliminary work assessing levels of HPV16 E7 DNA using quantitative PCR suggests that DMPA users have slightly higher levels than non-DMPA users (personal communication, Long Fu Xi). Upregulation of HPV gene expression by hormones may be an early stage event that occurs prior to viral integration27, 28
and other evidence suggests that once HPV is integrated hormones may have various effects depending on the placement of the hormone response elements.29
The fact that we did not find a positive association between hormonal contraception and ≥CIN2-3 could be explained, in part, by the fact that women enrolled in our study were relatively young and the duration of use was relatively short.
And third, hormones influence cervical epithelial differentiation and maturation.30–32
DMPA decreases cell maturation and promotes the appearance of atrophic epithelium30, 32
, which could make histologic features of CIN more difficult to detect among DMPA users because the loss of glycogen and hydration will shrink the cytoplasm lessening the effect of acetic acid.33
If the colposcopist cannot see the acetowhite lesions then she/he cannot do a directed biopsy. This may explain why among women with oncogenic HPV infection, DMPA use was inversely associated with CIN detection. However, this may not translate into an increased risk of developing invasive cervical cancer because the inverse association between DMPA and CIN was strongest for CIN1 lesions and most CIN1 lesions regress spontaneously. We have found that DMPA use did result in thinning of the vaginal epithelium perhaps reflecting the loss of glycogen.34
However, this association was not found in other studies.35–37
A limitation of this analysis is the use of self-reported data on hormonal contraceptive use, but there is no reason to suspect that accuracy differed between women with and without CIN because these data were obtained prior to colposcopy-biopsy. Additionally, studies comparing self-reported information to data from other sources have found good agreement for the current method and for total duration of use.38
We did not have information on the number of DMPA injections or if COC use was continuous during the time interval women reported using the method. Because of the young age of our population and their fewer years of contraceptive use, we had limited power to assess the association between long-term (≥10 years) hormonal contraceptive use and CIN and for several of the sub-analyses. Because women mostly used two similar types of COCs, we were also unable to look at the risk associated with specific formulations. Additionally, we did not have complete information on barrier contraception use. However, use of barrier contraception has not been consistently associated with protection from HPV infection.39, 40
There are several strengths of the current analysis. All subjects were ascertained from the same clinic population, and misclassification of disease status was minimized by 1) cases and controls being diagnosed in the same manner (by cytology and histology) and 2) requiring that the oncogenic HPV-positive/histologically negative group have negative and/or ASC-US cytology at both screening and colposcopy-biopsy. Lastly, we collected detailed information (brand/type, duration, date of last use) on the four most recent hormonal contraceptive methods. Only five women reported four methods so we are fairly confident that we sufficiently captured usage.
In summary, the hormonal contraception formulations used by women in this study do not appear to increase risk of ≥CIN2-3 or CIN1. Although women who use DMPA may be at an increased risk for HPV acquisition, neither the risk for persistent infection nor CIN was increased. Due to the tendency of DMPA to promote the appearance of an atrophic epithelium, it is also possible that the colposcopic and histologic features of HPV-related cervical lesions are less pronounced among women who use DMPA. If DMPA use makes lesions less visible, then this will be important for clinicians to take into account when performing colposcopies in women using this contraceptive method. Additionally, it will be important for future studies to evaluate the effects of long-term DMPA use and the current formulations of COC on HPV infection and cervical neoplasia.