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In page Cervical intraepithelial neoplasia:

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While retinoids are not effective in preventing the progression of CIN, they may be effective in causing regression of the disease in people with CIN2.[8] Therapeutic vaccines are currently undergoing clinical trials. The lifetime recurrence rate of CIN is about 20%,[citation needed] but it isn't clear what proportion of these cases are new infections rather than recurrences of the original infection.