Hypercalcemia in a patient with squamous cell carcinoma of the lung is mainly due to increased activity of which cell type?

In patients with squamous cell carcinoma of the lung, hypercalcemia often results from the secretion of parathyroid hormone-related peptide (PTHrP) by the tumor. PTHrP mimics the action of parathyroid hormone (PTH) and stimulates osteoclasts, leading to increased bone resorption. This process results in the release of calcium from the bones into the bloodstream, contributing to hypercalcemia.

Osteoclasts are specialized cells responsible for bone resorption, and their activity is crucial in conditions where calcium levels in the blood need to be modulated. In the case of malignancies such as squamous cell carcinoma, the tumor's secretion of substances like PTHrP enhances the osteoclast activity, causing elevated serum calcium levels.

Understanding this mechanism is vital in recognizing the paraneoplastic syndromes associated with certain cancers, particularly how malignancies can disrupt normal calcium metabolism through similar hormonal pathways. Thus, increased osteoclast activity in the context of malignancy-driven hypercalcemia is a key factor in the clinical presentation of patients with squamous cell lung carcinoma.