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osteolytic lesion

A softened section of a patient's bone formed as a symptom of specific diseases, such as breast cancer and multiple myeloma. This softened area appears as a hole on X-ray scans due to decreased bone density. In multiple myeloma, an increased number of myeloma cells block osteoblasts from creating new bone, while these cancerous cells also release factors that cause an upregulation on osteoclasts, causing an increasing in bone tissue resorption and an overall breakdown of bone integrity. This breakdown often begins in the bone marrow near tumor sites and spreads outward to the surface of the implicated bone. The most common cancers that metastasize to form osteolytic lesions are thyroid, lung, kidney, gastrointestinal, malignant melanoma, and breast, though any cancer can cause bone lesions. Lesions are most often found in larger bones, such as the skull, pelvis, radius, and femur. (Cause) Imbalance of regulatory factors in bone remodeling due to regulatory factors released by specific tumors. • Increased depletion and resorption of old bone tissue by osteoclasts. • Decrease in bone rebuilding by osteoblasts. (Regulation of bone remodeling) Systemic regulators • parathyroid hormone (PTH) • calcitriol • growth hormone • glucocorticoids • thyroid hormones • sex hormones Local regulators • cytokines • growth factors The over-activity of osteoclasts can also cause hypercalcemia, which can cause damage to the kidneys. Because it causes reduced glomerular filtration rate, increased sodium excretion and depletion of total body water, leading to increased bicarbonate reabsorption and metabolic alkalosis. Alkalosis enhances calcium reabsorption in the distal nephron, thus, aggravating the hypercalcemia.