Abstract P048

Tumor-associated macrophages correlate with skeletal involvement in classic Hodgkin lymphoma

Background: The biology of tumors spreading to bone is poorly understood, not least in classic Hodgkin lymphoma (cHL). When cHL disseminates, the newly affected sites typically harbor both Hodgkin and Reed-Sternberg cells along with cells from the tumor microenvironment (TME). However, whether cases presenting with bone lesions exhibit specific TME characteristics remains uncertain. We performed gene expression profiling (GEP) and immunohistochemistry (IHC) to characterize the TME of cHL with skeletal disease involvement at diagnosis.

Methods: GEP was conducted using the Nanostring nCounter Human 770 gene PanCancer Immune Profiling Panel on diagnostic lymph node biopsies from cHL patients with either no skeletal involvement (nodal only cHL, n-cHL; n=35), or skeletal involvement in addition to nodal disease (s-cHL; n=31). Differential protein expression of CD68, CD163, mannose receptor C-type 1 (MRC1/CD206), and CD20 were further evaluated by IHC in a larger cHL cohort (n=193).

Results: GEP revealed that at the time of diagnosis, samples from patients with s-cHL were rich in macrophage markers particularly CD163, CD206, macrophage receptor with collagenous structure (MARCO), and sialic acid binding Ig like lectin 1 (SIGLEC1) compared with samples from n-cHL. In contrast to the macrophage markers, genes encoding B-cell associated markers such as CD20, CD19, paired box 5 (PAX5), and CD79A/B were downregulated in s-cHL samples compared with n-cHL. We further evaluated the macrophage markers (CD68, CD163, and CD206) and the B cell marker CD20 at the protein level by IHC. All three macrophage markers had high expression levels in s-cHL compared with n-cHL (p<0.001, p<0.001, and p<0.001, respectively), whereas CD20 had low expression levels in s-cHL (p<0.001). The three macrophage markers correlated positively with each other (p<0.01) and Ann Arbor stage (p<0.001), while CD20 showed a negative correlation to stage (p<0.001).

Conclusion: Our data show different gene expression profiles in lymph node tumor samples from cHL with and without concomitant skeletal involvement at diagnosis. This suggests that tumors from patients with bone lesions show a unique TME molecular profile that could explain why some tumors seem to have a predisposition to disseminate to bone, and that tumor-associated macrophages and B cells could play a role in creating a pro-tumoral microenvironment facilitating the 'seed and soil' mechanism in the dissemination of disease in cHL.