ZEB1 and neoplasm: The lower PyMT mRNA levels indicate less CTCs in blood recovered from PyMT-Fib-cKO mice, as only circulating tumour cells express PyMT. Of note, PyMT mRNA levels were comparable in primary tumour cells (PTCs) from PyMT-Fib-cKO mice versus PyMT-cKO mice (Fig. 2j), suggesting that ZEB1 ablation does not affect PyMT expression.