p16 positive oropharyngeal squamous cell carcinoma:an entity with a favorable prognosis regardless of tumor HPV status

Abstract

Background: In the human papillomavirus (HPV) era, the best way to assess oropharyngeal squamous carcinomas (SCC) for risk stratification is not clear. Many recommend use of both p16 immunohistochemistry and HPV in situ hybridization (ISH). A significant minority of tumors are p16 positive and HPV ISH negative, the significance of which is unclear.

Methods: Two hundred thirty-nine oropharyngeal SCC were tested by immunohistochemistry for p16 and by ISH for high-risk HPV. For p16 positive, HPV ISH negative cases, PCR was conducted for HPV. The findings were correlated with pathologic and clinical findings.

Results: Of the 239 cases, 187 (78%) were positive for p16. Of these, 139 (74%) were positive for HPV by ISH. Of the remaining 48 cases, 45 had material for PCR. Nineteen were positive for HPV, leaving a group of 26 p16 positive and HPV undetectable SCCs. In the p16 positive cohort, there was no difference in survival between HPV ISH positive and negative cases. Comparing the HPV ISH positive and HPV ISH and PCR negative SCC, there was again no difference in survival. p16 positive, HPV negative SCC still had significantly better survival than p16 negative SCC in univariate and multivariate analysis.

Conclusions: Outcomes for p16 positive, HPV negative oropharyngeal SCC are not significantly different from p16 positive, HPV positive tumors and are significantly better than for p16 negative tumors. These results suggest that p16 immunohistochemistry alone is the best test to use for risk stratification in oropharyngeal SCC.

FIGURE 1

Typical histologic features of a nonkeratinizing (Type 3) SCC with well-circumscribed nests of tumor cells that have round to oval, hyperchromatic nuclei, minimal cytoplasm, and abundant apoptosis and mitotic activity. There is no surrounding stromal reaction. (H&E; 200 × magnification; SCC indicates squamous cell carcinoma).

FIGURE 2

Typical histologic features of a keratinizing-type (Type 1) SCC with angulated nests of tumor cells that have abundant, eosinophilic cytoplasm, well-defined cell borders, and round nuclei with vesicular chromatin and prominent nucleoli. This particular tumor also shows focal, frank keratinization. (H&E; 200 × magnification; SCC indicates squamous cell carcinoma).

FIGURE 3

Histologic features of a hybrid (Type 2) SCC that has areas of typical nonkeratinizing SCC with cells with minimal cytoplasm and oval, hyperchromatic nuclei combined with areas (more than 10% of the surface area) in which the tumor cells have abundant, eosinophilic cytoplasm, round nuclei with vesicular chromatin and nucleoli. (H&E; 200 × magnification; SCC indicates squamous cell carcinoma).

FIGURE 4

Cases segregated by test results. (+ indicates positive; −, negative; HPV, human papillomavirus; ISH, in-situ hybridization; PCR, polymerase chain reaction).

FIGURE 5

A, p16 IHC showing strong and diffuse nuclear and cytoplasmic expression in the tumor with minimal, patchy staining of normal surface mucosa (200 magnification). B, HPV ISH showing a SCC with no evidence of blue staining and thus no evidence of HPV (200 × magnification) (HPV indicates human papillomavirus; IHC, immunohistochemistry; ISH, in-situ hybridization; SCC, squamous cell carcinoma).

FIGURE 6

Survival curves for testing subgroups. A, Overall survival—p16 positive, HPV ISH positive versus p16 positive, ISH negative versus p16 negative, HPV negative SCC. B, Overall survival—p16 positive, HPV ISH positive versus p16 positive, ISH and PCR negative versus p16 negative, HPV negative SCC. C, Disease-free survival—p16 positive, HPV ISH positive versus p16 positive, ISH negative versus p16 negative, HPV negative SCC. D, Disease-free survival—p16 positive, HPV ISH positive versus p16 positive, ISH and PCR negative versus p16 negative, HPV negative SCC. E, Disease-specific survival—p16 positive, HPV ISH positive versus p16 positive, ISH negative versus p16 negative, HPV negative SCC. F, Disease-specific survival—p16 positive, HPV ISH positive versus p16 positive, ISH and PCR negative versus p16 negative, HPV negative SCC. (HPV indicates human papillomavirus; ISH, in-situ hybridization; PCR, polymerase chain reaction; SCC, squamous cell carcinoma).