Anal intraepithelial neoplasia, AIN

Human papilloma virus is a major factor in the aetiology of anal intraepithelial neoplasia.

Epidemiology

The incidence of both anal intraepithelial neoplasia and invasive carcinoma is increasing in sexually active homosexual men.

Immunohistochemistry

p16 and Ki67 may be useful in the identification of AIN:

			Normal	Condyloma	AIN I	AIN II	AIN III
	p16	spotty staining of more than 10% of squamous cells (staining in scattered cells at any level of the epithelium)	3/371	1/121	2/141	3/251	2/161
		contiguous staining of more than 90% of squamous cells	1/37 (staining in the one positive case was confined to the lower third of the epithelium)1	0/121	3/14 (staining confined to the lower third of the epithelium)1	20/25 (staining is seen in at least the lower two thirds of the epithelium)1	14/16 (staining is seen in at least the lower two thirds of the epithelium)1
	Ki67	<25% positive nuclei	35/371	7/121	6/141	3/251	1/161
		25-50% positive nuclei	3/271	5/121	4/141	10/251	3/161
		50-75% positive nuclei			4/141	7/251	7/161
		75-100% positive nuclei				5/251	5/161

References

¹ Walts AE, Lechago J,Bose S. P16 and Ki67 Immunostaining is a Useful Adjunct in the Assessment of Biopsies for HPV-Associated Anal Intraepithelial Neoplasia. Am J Surg Pathol 2006; 30:795-801

This page last revised 23.7.2006.

©SMUHT/PW Bishop