(a) IHC staining performed on formalin-fixed, paraffin-embedded (FFPE) tissue sections revealed diffusely positive H3K9me2 and H3K9me3 staining across PDAC cells from the founder clone (top), the subclone that seeded metastasis (middle), and the peritoneal metastasis (bottom) in patient A141. Scale bars, 100 μm. (b) In contrast, heterogeneous staining for H3K9me2 and H3K9me3 was detected in FFPE tissue sections taken from the primary tumor subclone that seeded metastasis (middle) and in the matched liver metastasis itself (bottom) in patient A132. Scale bars, 100 μm. (c) FFPE tissue sections were available from primary tumor subclones that seeded both peritoneal and distant metastasis in patient A38. Similar to patients A124 (Fig. 1a) and A141, diffusely positive staining for heterochromatin modifications was observed in both the founder clone (first panel) and the subclone that seeded peritoneal metastasis (second panel). In contrast, similar to patients A125 (Fig. 1b) and A132, heterogeneous staining between PDAC cells emerged in the primary tumor subclone that seeded distant metastases (third panel). The matched lung metastasis itself was diffusely negative (fourth panel), similar to cell lines isolated from this site and a matched liver metastasis in this patient (Fig. 1c). Scale bars, 100 μm. (d) Immunoblots on cell lines showed minimal or inconsistent changes for the indicated histone modifications between regional PDAC samples, including A38Per (Per). (e) In contrast, immunoblots on cell lines isolated from a panel of distant metastatic subclones showed recurrent changes in specific modifications, as compared to A38Per. (f) Global reprogramming of H3K9me3 and H4K20me2 was also observed between cell lines isolated from primary tumor subclones (Pr1, Pr2) and a matched lung metastasis in the same patient (pA13).