Characterization of Cancer Stem Cells in Olfactory Neuroblastoma Identifies Increased PD-L1 Expression

Background: Olfactory neuroblastoma (ONB), also known as esthesioneuroblastoma, is a rare malignant neoplasm arising from the olfactory neuroepithelium. While the five-year survival rate for ONB is around 69%, there is a poorer prognosis for patients with recurrent or metastatic disease with limited treatment options. Cancer stem cells (CSCs) are self-renewing oncogenic cells that drive tumor progression, proliferation, and recurrence. The objective of this study was to characterize CSC density and PDL1 expression in ONB using multispectral immunofluorescence (mxIF) and evaluate whether this cell population correlates with recurrent or high-grade disease.

Methods: Formalin-fixed, paraffin-embedded (FFPE) tissue microarray (TMA) including 47 clinically annotated human ONB samples in triplicate was obtained, with IRB approval, from our tertiary care hospital. A cancer stem cell panel was validated in ONB tissue. The TMA was stained for CD15, CD24, ALDH1A1, PDL1, synaptophysin and DAPI with the CSCs being positive for CD15, CD24, ALDH1A1, and synaptophysin. Characterization of the TMA slides was manually performed using HALO image analysis platform v3.5 to objectively identify CSCs. A retrospective chart review was performed from these clinically annotated specimens with collection of patient demographics, Hyams grade, Kadish stage, recurrence, and survival.

Results: Twenty-seven samples were included in the final analysis, as twenty samples had too little tumor content for analysis of this rare cell population. The average age at diagnosis was 54 years with a majority of the patients being male (63%). Seven out of twenty-seven patients had high Hyams grade tumors (III/IV) and 22 out of 27 patients had high Kadish stage tumors (C/D). Thirty percent of patients went on to have a recurrence. On average, 0.08% of ONB cells were CSCs ([Figs. 1] and [2]). The median CSC density was 12.7 cells per mm² of tumor parenchyma. There was no difference in quantities of CSCs between low and high Hyams grade tumors (p = 1.00) or low and high Kadish stage tumors (p = 0.165). Patient demographics, incidence of recurrence or survival also did not correlate with CSC density. However, interestingly there was a significant difference in the median number of PDL1 + CSCs versus PDL1-CSCs (6.7 vs. 0.67, p < 0.001). No differences were noted when comparing the PDL1 + CSCs for Hyams grade, Kadish stage, recurrence or survival.

Conclusion: This study evaluated the presence of CSCs in ONB and sought to determine whether this correlated with invasion, progression, and recurrence. While CSCs are present in ONB, they are uncommon, and no correlation with grade, stage, or recurrence was observed. A significant amount of the CSCs are PDL1+, revealing a potential immunotherapy strategy for ONB by targeting this particular cell population through PD-1/PDL1 immune checkpoint blockade.

Fig. 1 CSC in ONB, red arrow indicates CSC.

Fig. 2 CSC panel for ONB.

Publication History

Article published online:
05 February 2024