HTRA1 and metastatic malignant neoplasm: Subsequent studies have also reported that HTRA1 expression is decreased in different types of cancers, including metastatic cancers.47, 48, 49, 50, 51, 52 An early study on ovarian cancer has suggested a high frequency of loss of heterozygosity near HTRA1 may be associated with its decreased expression in cancer cells.49 Many signalling pathways in tumour progression are regulated by HTRA1 via proteolysis.