Figure 1. BC PDX models show varying metastatic potential.

(A) Experimental overview: Lung metastases and primary tumor tissues were isolated from orthotopically transplanted BC PDX models and dissociated. The resulting single-cell suspensions were FACS enriched for human cells using a human specific antibody (hCD298) and sorted into 384-well plates (1 cell per well), and scRNA-Seq was performed using Smart-Seq2. Data analysis investigated tumor heterogeneity and differences between primary tumor and metastatic cells. (B) Bar chart shows the median number of metastatic foci per mm² lung tissue area per model (upper panel), determined by histology. Metastatic foci were classified as micrometastasis (< 10 cells), intermediate (10–100 cells), and macrometastasis (>100 cells). Box plot shows the fraction of metastatic tissue per total lung tissue area, determined by histology (lower panel). The x-axis shows the model, BC subtype, and metastatic potential. (C) Representative H&E-stained images of metastatic lung tissue for low, moderate, and high metastatic potential models. Scale bars: 100 μm. (D) Bubble plot showing the expression of receptors in primary tumor (PT) and metastatic cells (Met) per model. (E) Representative images showing immunohistochemical staining for ER, PR, and HER2 in primary tumors and metastatic lungs of ER⁺ tumor models. Arrowheads indicate metastasis. When possible, the same metastasis is shown in consecutive sections. Scale bars: 100 μm.