Cutaneous Squamous Cell Carcinoma – High-Risk Features and Prognostic Factors

A 62-year-old man with a 10-year history of actinic keratosis presents with a rapidly enlarging, indurated nodule on the dorsum of his hand with central ulceration and rolled edges. Dermoscopy reveals a white-to-yellow core with surrounding erythema and telangiectasia. Histopathology shows infiltrative growth pattern with perineural invasion and desmoplasia. Which of the following is the MOST important prognostic factor that would necessitate wider surgical margins and consideration of adjuvant therapy in this case?