Breast implant associated anaplastic large cell lymphoma is a heterogeneous T cell disease with active pro-tumour cross-talk and immune suppression.

Breast implant-associated anaplastic large cell lymphoma (BIA-ALCL) is a rare T cell lymphoma in women with textured implants. Little is known about the cell of origin (COO) and whether the tumour immune microenvironment (TIME) is critical for BIA-ALCL survival. Single-cell RNA sequencing revealed BIA-ALCL cells were heterogeneous with unique gene profiles per patient and signature genes BATF3, SERPINS, TNFSFR8, and IL2RA. The COO is a CD4+ or CD8+ memory T cell identified through rearranged TCR and gene expression. The BIA-ALCL TIME included distinct myeloid clusters, dendritic cells (DCs), and monocytes, which may support lymphoma cells. Cytokines IL-13, IL-10, TNF and secretory PDL1 were increased in BIA-ALCL seroma, indicating an immunosuppressive TIME. Interactome analysis revealed a complex network among lymphoma cells, dominated by IL-13, IL-10, and TNF members. Endogenous CD8+ T cells exhibit higher checkpoint expression than benign seromas. No clonal relationship exists between BIA-ALCL and endogenous T cells. Tissue-archetype and gene-expression analysis revealed T-cell exclusion and immunosuppressive TIME in invasive disease. In summary, BIA-ALCL cells are diverse with markedly different TIME across stages. The TIME provides immunosuppressive signals to activated/exhausted T cells and homeostatic signals that promote BIA-ALCL proliferation. These new findings may offer novel therapeutic targets for advanced disease patients.