To our knowledge, this is the first study to report estimates of completeness for the registration of VIN and VaIN at a Cancer Registry. We can therefore only compare our estimates to those reported for cancers. Larsen et al. [9
] estimated the average completeness of invasive vulvar and vaginal cancer incidence registration at CRN to be 99.8% [9
]. Our estimates of completeness for the period 2002 to 2007 for VIN and VaIN were 95.0% and 92.9%, respectively, with some variation between years. One reason for the somewhat lower completeness of premalignant lesions than of cancer may be that some cancers are obtained from death certificates. Cancer mentioned on the death certificate allows CRN to send a reminder to the hospitals that have not yet reported a new cancer case [9
]. It should also be noted that there is some uncertainty in the completeness estimates reported here since the pathology laboratories during re-collection of notifications did not manage to identify at least 573 notifications that were previously registered as VIN or VaIN in the CRN database. It is thus possible that they also may have failed to submit notifications not already registered by the CRN. The highest percentage of notifications missing in the CRN database occurred in 2007. This may indicate that a small proportion of the 2007 notifications were not yet registered in the database at CRN at the time of data extraction. This is in line with the observation that timeliness for VIN and VaIN was 267 days in 2006, compared to 445 days in 2007. The registration of a subset of VIN and VaIN notifications from 2007 was put on hold due to internal priorities at CRN and may explain some of the increase. The time interval from diagnosis to the notifications is sent to CRN by the pathology laboratories could be another source of variation in timeliness.
A total of 184 lesions that were assigned skin SNOMED topography codes by the pathology laboratories were coded to vulva topography by the medical coders at the CRN. This highlights the importance of a national cancer registry that can harmonise the coding practices of local pathology laboratories. Moreover, it illustrates how discrepancies in coding practices may influence completeness estimates in quality assessments of disease registration.
A VIN or VaIN lesion in a patient with a prior premalignant or malignant lesion in a nearby site has generally been assigned to the topography of the primary registration by the CRN medical coders. This has led to fewer registrations of VaIN in particular. A reason is that far more lesions occur in the cervix [21
] and it is therefore more likely that a VaIN lesion has been assigned to the cervix than a cervical lesion has been assigned to the vagina. We have changed the coding practice at CRN so that VaIN and VIN cases are assigned topography codes according to the site of the lesion, regardless of disease history at other anatomical locations. The change took effect in 2009, and we will also recode retrospectively for the years 2002 to 2008. We believe that this change of practice will give us more reliable data to monitor the results of HPV vaccinations on the incidence of HPV-related diseases of the vulva and vagina. This change of coding practice affected 44 notifications with lesions originally assigned cervical topography code, but during the reabstraction assigned vaginal topography code. These were not included in the estimation of the accuracy of topography codes assigned to notifications at CRN and reabstracted notifications.
We have modified the published definitions of the severity of misclassification of cancers to evaluate the accuracy in registration of premalignant lesions. In brief, a major discrepancy as opposed to a minor discrepancy affects the incidence rates of VIN and VaIN. We could not compare the accuracy of the CRN coding of VIN and VaIN to other cancer registries since no such data, to our knowledge, has been published.
We found that 9.1% of the notifications had a minor discrepancy between the original and reabstracted morphology codes. Minor discrepancies occurred even though rules for giving priority to some codes over others exist for diagnoses with more than one appropriate morphology code. The majority of minor discrepancies occurred on notifications describing VIN 3/VaIN 3, carcinoma in situ and severe atypia/dysplasia in squamous epithelial cells for which there are separate morphology codes. The number of minor discrepancies should be reduced to a minimum by changing the coding practice. This entails using fewer morphology codes.
The fact that 1.5% VIN and 2.2% VaIN of all notifications had a major discrepancy between the original and reabstracted morphology and topography codes, indicate that major misclassification is not a significant problem in the registration of high grade VINandValN.
The selection of morphology codes used in this evaluation of data quality was chosen to assess the feasibility of the CRN to effectively monitor how HPV vaccination programmes will impact on the incidence of HPV-related premalignant diseases of the vulva and vagina. The present analysis indicates that the comparability, completeness, validity and timeliness of high grade VIN and VaIN registration is satisfactory, and therefore that the Cancer Registry of Norway is able to monitor high grade vulvar intraepithelial and vaginal intraepithelial neoplasias with adequate precision.