Chemoprevention of Head and Neck Cancers: Does It Have Only One Face?

Table 2

Retinoids and compounds blocking their metabolism used in therapy or clinical studies.

	Retinoids and compounds blocking their metabolism
1.	Retinoids of natural origin (first generation of retinoids)
	(i) Retinol
	(ii) Retinaldehyde
	(iii) Retinoic acid
	(a) All-trans-retinoic acid (ATRA)
	(b) 9-cis retinoic acid
	(c) 13-cis retinoic acid (tretinoin, isotretinoin, alitretinoin)
2.	Synthetic monoaromatic retinoids (second generation of retinoids)
	(i) Acitretin
	(ii) Etretinate (withdrawn from the market)
	(iii) Motretinid
3.	Synthetic poliaromatic retinoids (third generation of retinoids)
	(i) Adapalene
	(ii) Tazaroten
	(iii) Bexarotene
4.	Atypic retinoids
	(i) Fenretinide (4-HPR; N-(4-hydroxyphenyl)retinamide)
5.	Retinoic acid metabolism blocking agents (RAMBAs)
	(i) Liarozole (inhibitor of cytochrome p450 acid 4-hydroxylase)