The cancers of the vulva and birth canal typically develop over a long period of time. Normal cells under go a transition to cancer and this stage is described as pre-cancerous. This represents an opportunity to prevent the development of cancer. The precancerous lesions in the vulvar are described as vulvar intraepithelial neoplasia (VIN) and in the birth canal (BC) it is described as VAIN.
Previously the precancerous changes in the vulvar were classified as VIN 1-3 but this was changed in 2004. There was a lack of evidence supporting VIN 1 as a precancerous lesion that required treatment. VIN now is reserved for a description of high-grade lesions and is now classified as VIN usual type and VIN differentiated type. The usual type includes the warty and basaloid types as well as those that have features of both. The usual type is associated with human papilloma virus (HPV) while the differentiated type is not associated with HPV. Unclassified is used to describe the lesions that donít fit into either category.
VAIN represents precancerous changes or squamous cell atypia of the tissue of the BC. VAIN 1 is present when the lower 1/3 of the cells are affected, VAIN 2 when 2/3 of the thickness is involved and VAIN 3 is when more than 2/3 of the tissue thickness has atypical cells. VAIN 3 is also described as carcinoma in-situ and the next step would be invasive cancer. VAIN is much less common than VIN or CIN (cervical intraeptithelial neoplasia.
The risk factors for VIN usual type and VAIN are the same. They include infection with HPV, smoking and immunosuppression. HPV types 16, 18 and 31 are the oncogenic types and are associated with the high-grade lesions while types 6 and 11 are associated with the lesions previously classified as VIN 1. The risk factors for differentiated VIN are the same as those for HPV negative vulvar cancer and tend to be older age and a history of vulvar dystrophies.
The precancerous lesions associated with HPV infection tend to be multifocal and multicentric. If these lesions are found in one site then there is a good chance that they are present in other areas of the female genital tract. Sixty percent of women with VIN or VAIN will also have CIN while 10% of women with CIN 3 will have VIN or VAIN.
Once a diagnosis of VIN and VAIN is made, then immediate treatment is indicated to prevent the development of cancer. This diagnosis also suggests an increased risk for similar lesions in the cervix, so a screening pap and/or HPV testing is indicated. Early detection is the key to prevent cancer of the female genital tract.
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