Three BC (high KRT14 and KRT5 expression) [32–34], three SC (high S100A8 or KRT6A expression) [35], and three GC (high CLDN4, CLDN1, or DLK2 expression) [30, 31, 36] cell subtypes were discovered in the rumen (Fig. 2D, E). Here, KRT5 is linked to breast cancer.