SummaryThe metastatic process of colorectal cancer (CRC) is not fully understood and effective therapies are lacking. We show that activation of NOTCH1 signaling in the murine intestinal epithelium leads to highly penetrant metastasis (100% metastasis; with >80% liver metastases) in KrasG12D-driven serrated cancer. Transcriptional profiling reveals that epithelial NOTCH1 signaling creates a tumor microenvironment (TME) reminiscent of poorly prognostic human CRC subtypes (CMS4 and CRIS-B), and drives metastasis through transforming growth factor (TGF) β-dependent neutrophil recruitment. Importantly, inhibition of this recruitment with clinically relevant therapeutic agents blocks metastasis. We propose that NOTCH1 signaling is key to CRC progression and should be exploited clinically.

(1) Background: an increasing number of breast cancer patients develop lethal brain metastases (BM). The complete removal of these tumors by surgery becomes complicated when cells infiltrate into the brain parenchyma. However, little is known about the nature of these invading cells in breast cancer brain metastasis (BCBM). (2) Methods: we use intravital microscopy through a cranial window to study the behavior of invading cells in a mouse model of BCBM. (3) Results: we demonstrate that BCBM cells that escape from the metastatic mass and infiltrate into brain parenchyma undergo epithelial-to-mesenchymal transition (EMT). Moreover, cells undergoing EMT revert to an epithelial state when growing tumor masses in the brain. Lastly, through multiplex immunohistochemistry, we confirm the presence of these infiltrative cells in EMT in patient samples. (4) Conclusions: together, our data identify the critical role of EMT in the invasive behavior of BCBM, which warrants further consideration to target those cells when treating BCBM.

The pro-tumourigenic role of epithelial TGFβ signalling in colorectal cancer (CRC) is controversial. Here, we identify a cohort of born to be bad early-stage (T1) colorectal tumours, with aggressive features and a propensity to disseminate early, that are characterised by high epithelial cell-intrinsic TGFβ signalling. In the presence of concurrent Apc and Kras mutations, activation of epithelial TGFβ signalling rampantly accelerates tumourigenesis and share transcriptional signatures with those of the born to be bad T1 human tumours and predicts recurrence in stage II CRC. Mechanistically, epithelial TGFβ signalling induces a growth-promoting EGFR-signalling module that synergises with mutant APC and KRAS to drive MAPK signalling that re-sensitise tumour cells to MEK and/or EGFR inhibitors. Together, we identify epithelial TGFβ signalling both as a determinant of early dissemination and a potential therapeutic vulnerability of CRC’s with born to be bad traits.