Interpretation of HPV DNA in situ hybridization in HPV-related head and neck squamous cell carcinoma: an achievable task in cell block and small biopsy material

Introduction Human papilloma virus (HPV)-related head and neck squamous cell carcinoma (HNSCC) is a distinct entity with a better prognosis than conventional disease. Therefore, an accurate and reproducible HPV test is needed. Herein, the analytical factors and interpretation of the HPV DNA in-situ hybridization (ISH) test are investigated. Materials and methods We evaluated 63 ultrasound-guided fine-needle aspiration (FNA) HNSCC cases for a semi-quantitative assessment of the ease of interpretation, staining pattern, and highest magnification needed for HPV DNA ISH on cell block and core biopsy. Results A total of 72 HPV DNA ISH tests were performed in 59 (93.6%) cases. Of these, 17 had more than one HPV DNA ISH assays and 4 (6.4%) had no HPV tests. At least one HPV stain was positive in 38 (62.2%) cases. Eleven (28.95%) ISH tests were rated as difficult or moderately difficult to interpret, and 27 (78.05%) were rated as easy or moderately easy. Twenty-four (63.2%) ISH tests demonstrated strong staining and 14 (36.8%) demonstrated weak staining. Twenty-seven (71.1%) stained diffusely, and 11 (29.0%) focally. Twenty-seven ISH tests required 400× or higher magnification for interpretation. Background debris and nonspecific staining were present in 25 (35.7%) and 15 (21.4%) HPV DNA ISH cases, respectively. p16/HPV ISH was discrepant in 4 (7.3%) cases (3 P16+/HPV−, and 1 p16−/HPV+). Conclusions HPV DNA ISH interpretation can be challenging because of focal or weak staining, which requires careful examination at high magnification. An alternate method is needed for DNA ISH−/p16+ cases.