1)                    Chronic immunosuppression [8, 43]

2)                    Deep invasion (> 4 mm) [8, 45]

3)                    High grade or desmoplastic lesions [8, 45]

4)                    Incomplete excision and recurrence of the primary tumor [6, 8, 9, 54, 55]

5)                    Large lesions (> 2 cm) [6, 8, 45]

6)                    Lesions located within the lymphatic drainage of the parotid gland or those on the lower lip [56, 57, 58, 59, 60]

7)                    Occurrence in non sun-exposed areas [4, 8]

8)                    Perineural invasion [45, 61]

9)                    Precursor lesion of Actinic Keratosis [14, 16, 17]