Cancer can be difficult to diagnose and can be considered a "great imitator. "People may become anxious or depressed post-diagnosis. The risk of suicide in people with cancer is approximately double. Local symptoms
Local symptoms may occur due to the mass of the tumor or its ulceration. For example, mass effects from lung cancer can block the bronchus resulting in cough or pneumonia; esophageal cancer can cause narrowing of the esophagus, making it difficult or painful to swallow; and colorectal cancer may lead to narrowing or blockages in the bowel, affecting bowel habits. Masses in breasts or testicles may produce observable lumps. Ulceration can cause bleeding that can lead to symptoms such as coughing up blood (lung cancer), anemia or rectal bleeding (colon cancer), blood in the urine (bladder cancer), or abnormal vaginal bleeding (endometrial or cervical cancer). Although localized pain may occur in advanced cancer, the initial tumor is usually painless. Some cancers can cause a buildup of fluid within the chest or abdomen. Systemic symptoms
Systemic symptoms may occur due to the bodys response to the cancer. This may include fatigue, unintentional weight loss, or skin changes. Some cancers can cause a systemic inflammatory state that leads to ongoing muscle loss and weakness, known as cachexia.Some cancers, such as Hodgkins disease, leukemias, and liver or kidney cancers, can cause a persistent fever.Some systemic symptoms of cancer are caused by hormones or other molecules produced by the tumor, known as paraneoplastic syndromes.
Mutations in the cathepsin K gene are associated with pycnodysostosis, a hereditary osteopetrotic disease, characterised by a lack of functional cathepsin K expression. Knockout studies of cathepsin K in mice lead to an osteopetrotic phenotype, which, is partially compensated by increased expression of proteases other that cathepsin K and enhanced osteoclastogenesis. Cathepsin K has an optimal enzymatic activity in acidic conditions. It is synthesized as a proenzyme with a molecular weight of 37kDa, and upon activation by autocatalytic cleavage, is transformed into the mature, active form with a molecular weight of ~27kDa. Upon polarization of the osteoclast over the site of resorption, cathepsin K is secreted from the ruffled border into the resorptive pit. Cathepsin K transmigrates across the ruffled border by intercellular vesicles and is then released by the functional secretory domain. Within these intercellular vesicles, cathepsin K, along with reactive oxygen species generated by TRAP, further degrades the bone extracellular matrix. Several other cathepsins are expressed in osteoclasts including cathepsins B, C, D, E, G, and L.  The function of these cysteine and aspartic proteases is generally unknown within bone, and they are expressed at much lower levels than cathepsin K.
Studies on cathepsin L knockout mice have been mixed, with a report of reduced trabecular bone in homozygous and heterozygous cathepsin L knockout mice compared to wild-type and another report finding no skeletal abnormalities. Matrix metalloproteinases
The matrix metalloproteinases (MMPs) comprise a family of more than 20 zinc-dependent endopeptidases.