PTH like substance is produced by which type of lung malignacy –
**Core Concept**
The question is testing the student's knowledge of a rare paraneoplastic syndrome associated with lung malignancies. Paraneoplastic syndromes are clinical disorders caused by substances produced by tumor cells that have effects on distant organs. In this case, the substance in question is a PTH-like substance, which is likely a parathyroid hormone-related protein (PTHrP).
**Why the Correct Answer is Right**
PTHrP is a protein that mimics the action of parathyroid hormone (PTH) by stimulating osteoclasts to break down bone, leading to hypercalcemia. This is a characteristic feature of humoral hypercalcemia of malignancy (HHM), a paraneoplastic syndrome associated with certain types of cancer, including squamous cell carcinoma of the lung. The production of PTHrP by tumor cells leads to increased calcium levels in the blood, which can cause a range of symptoms including weakness, fatigue, and renal impairment.
**Why Each Wrong Option is Incorrect**
* **Option A:** is incorrect because while small cell carcinoma of the lung can cause a range of paraneoplastic syndromes, it is not typically associated with PTHrP production.
* **Option B:** is incorrect because while lung cancer can cause hypercalcemia, it is not always due to PTHrP production.
* **Option C:** is incorrect because while squamous cell carcinoma of the lung is a common type of lung cancer, it is not the only type that can produce PTHrP.
**Clinical Pearl / High-Yield Fact**
PTHrP is a tumor-produced hormone that can cause hypercalcemia by stimulating osteoclasts to break down bone. This is a key point to remember when evaluating patients with lung cancer and hypercalcemia.
**Correct Answer:** C. Squamous cell carcinoma of the lung is the most common type of lung cancer associated with PTHrP production.