Commonest site for spread of the cancers is:

**Core Concept**
The question is testing knowledge of the lymphatic system's role in cancer spread, specifically the commonest site for metastasis. The lymphatic system is a network of vessels, nodes, and organs that help defend the body against infection and disease, including cancer.

**Why the Correct Answer is Right**
The correct answer is related to the concept of lymphatic drainage, where cancer cells can spread from the primary tumor site to regional lymph nodes. The lymphatic system's capillary network is the primary route for cancer cells to migrate from the tumor site to the nearest lymph nodes. The most common site for cancer spread is the first echelon lymph node, which is the first lymph node to receive lymphatic drainage from the primary tumor site. This is because the cancer cells are carried through the lymphatic capillaries to the nearest lymph node, where they can then invade and establish a new tumor.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because the first echelon lymph node is not necessarily the first lymph node to be involved in every cancer case. The specific lymph node involved can depend on various factors, including the location of the primary tumor.
* **Option B:** This option is incorrect because while the lymphatic system plays a crucial role in cancer spread, the liver is not the most common site for cancer metastasis.
* **Option C:** This option is incorrect because while the lungs are a common site for cancer metastasis, they are not the primary site for the initial spread of cancer cells.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that the first echelon lymph node is the most common site for cancer spread, and it is often the first site to be involved in a cancer case. This is because the lymphatic system's capillary network provides a direct route for cancer cells to migrate from the primary tumor site to the nearest lymph node.

**Correct Answer: C. Lungs.**