Supplementary Material for: High-Frequency Ultrasound Quantification of Endophytic Growth Pattern: A Potential Imaging Indicator for Grading Cutaneous Squamous Cell Carcinoma Differentiation

Background: Cutaneous squamous cell carcinoma (cSCC) is the second most common type of skin cancer. While most tumors have a positive prognosis, poorly-differentiated tumors increase the risk of negative outcomes. Few studies are available on non-invasive methods to determine the level of differentiation of cSCC before surgery.
Objective: To determine the degree of differentiation of cSCC using high-frequency ultrasound (HFUS).
Methods: This study included 117 lesions from 117 patients, of which 68 were well-differentiated cSCC, 30 were moderately-differentiated and 19 were poorly-differentiated. We analyzed the clinical, appearance, histopathological and HFUS characteristics of cSCC. The thickness characteristics measured by HFUS included the overall thickness of the tumor, the thickness of the tumor's endophytic part , and the proportion of endophytic thickness to the overall thickness.
Results: The three groups did not show significant differences in their clinical and appearance features (all P > 0.017). However, on HFUS, the lesion total thickness, endophytic proportion and surface keratinization were the significant features for identifying poorly-differentiated cSCC. While a single indicator is not as effective as the combination of all three (all P > 0.05), the diagnostic accuracy of any two or all three indicators together did not show significant differences (P < 0.05).
Conclusions: HFUS can reveal internal morphological details of cSCC lesions, identifying poorly-differentiated cSCC by analyzing total lesion thickness, endophytic proportion, and surface hyperkeratinization. Any two of these features can be as effective as using all three to diagnose poorly-differentiated cSCC.