5. Clinical features defining high risk of relapse include infiltrative growth margins, size, tumor location, histological subtype (the morpheaform, the sclerosing, the infiltrating, the micronodular and the metatypical subtypes are associated with higher risk of relapse as compared to the risk associated with the superficial and the nodular types), recurrent-refractory tumors (see Table 1), basal cell carcinoma size (largest tumor diameter) ≤ 5 cm for head and neck tumors