Accentuated p53 staining in usual type vulvar dysplasia-A potential diagnostic pitfall

Evaluation of vulvar intraepithelial neoplasia (VIN) may be difficult due to overlapping histologic features seen in both usual (UVIN) and differentiated vulvar intraepithelial neoplasia (DVIN). DVIN represents a diagnostic challenge; poor inter-observer agreement is well documented. P53 has been described as a potentially helpful adjunct in some cases; however, intricacies in its interpretation remain. This study evaluated 41 consecutive cases which consisted of 23 keratinizing dysplasias that were morphologically suggestive of DVIN and 18 UVINs. All cases were stained with p16 and p53. Our results revealed that 22 of 41 (54%) VINs showed novel accentuated wild type (WT) staining with non-linear basal staining for p53, including 12 (52%) cases histologically suggestive of DVIN and 10 (56%) described as UVIN. P16 was positive in 100% of the accentuated wild type cases, consistent with a diagnosis of UVIN. Positive p53 and negative p16 staining was seen in 4 (17%) cases histologically suggestive of DVIN. Of these, 75% progressed to carcinoma, whereas only 1 of 35 (3%) patients with UVIN progressed to carcinoma. In conclusion, DVIN is difficult to diagnose due to potential histologic overlap with UVIN, especially the warty, or keratinizing, subtype. Accentuated WT p53 in absence of concurrent p16 staining may lead to misdiagnosis of DVIN, especially in small biopsy samples. P16/p53 staining should be performed in tandem with strict adherence to patterns considered positive, as patients with UVIN have significantly less risk of progression.