Purpose: p105 is a proliferation-associated nuclear antigen which identifies proliferating but not resting cells. The objectives of this Radiation Therapy Oncology Group (RTOG) protocol (91-08) were: (1) to correlate tumor proliferative potential estimated using the p105 assay and deoxyribonucleic acid (DNA) analysis with treatment outcome in patients irradiated for advanced squamous cell carcinoma of the head and neck; and (2) to evaluate the potential of p105 labeling indices as a predictive assay.
Methods and materials: Paraffin blocks of pretreatment biopsies of the primary tumor or metastatic neck nodes of patients with Stage III or IV squamous cell carcinoma of the head and neck treated with radiotherapy alone in three previous RTOG protocols (79-13, 79-15, and 83-13) were retrospectively obtained. From these paraffin blocks, areas of tumor were selected based on histological examinations and sectioned. Nuclei suspensions were then prepared and processed for p105 antibody and DNA staining and subsequent flow cytometric quantification of p105 labeling indices and DNA content and correlation with local-regional control and survival.
Results: Paraffin blocks of tumor biopsies from 148 out of a total of 598 eligible patients were available. Of these, 143 were analyzable. The median and (range) of p105 labeling index (LI-C), p105 labeling index of cells in S phase (LI-S), and p105 antigen density (AD) were: 66.6 (3.85-99.5), 9 (1.55-36), and 93.2 (7.4-628.5), respectively. Deoxyribonucleic acid was diploid in 67 (47%), aneuploid in 22 (15%) and mixed aneuploid/diploid in 54 (38%) patients. There was a strong correlation between AD and DNA ploidy. Antigen density was above median in 91.5% of the aneuploid or mixed aneuploid/diploid tumors, but only in 8.5% of the diploid tumors. Patients with aneuploid or mixed aneuploid/diploid tumors had significantly greater local-regional failures than patients with diploid tumors (p = .0180). Those with p105 LI-C below the median or p105 AD above the median also had significantly greater local-regional failures (p = .0500 and p = .0167, respectively). Patients with p105 AD below the median had significantly better survival than those above the median (p = .0444), although there was no significant difference in survival with respect to DNA ploidy or p105 LI-C. Multivariate analyses showed that T-stage (p = .0001) and p105 AD (p = .0044) were significant prognostic factors for local-regional control, and T-stage (p = .0080), N-stage (p = .0021), primary site (p = .0110), and p105 AD (p = .0326) were significant prognostic factors for survival.
Conclusion: These results suggest that flow cytometric quantitation of the proliferation-associated nuclear antigen p105 and DNA content of pretreatment tumor biopsies may be a potentially useful predictive assay in patients irradiated for advanced squamous cell carcinomas of the head and neck.