For example, Porphyromonas gingivalis, associated with oral cancer progression, actively triggers the transcription of α-defensins in oral tumor cells, which in turn is thought to promote the proliferation of these cells.389 In contrast, HD5 and HD6 are protective against colon cancer.404–406 For example, HD5 expression is reduced in colon cancer tissues from patients, and prognostic results indicate that patients with high HD5 expression have significantly longer survival than patients with low HD5 expression.405 HD5 overexpression also inhibits tumor growth in nude mice. This evidence concerns the gene DEFA5 and malignant colon neoplasm.