**Core Concept**
Reed-Sternberg cells are distinctive, multinucleated giant cells seen in a specific type of lymphoma. They are a hallmark of classical Hodgkin lymphoma (cHL), a type of cancer that affects the immune system. The presence of these cells is a key diagnostic feature of cHL.

**Why the Correct Answer is Right**
Reed-Sternberg cells are characterized by their large size, abundant cytoplasm, and two or more prominent nuclei with prominent nucleoli. They are thought to arise from transformed germinal center B cells, and their presence is often accompanied by a mixed inflammatory infiltrate of lymphocytes, eosinophils, and plasma cells. The exact mechanism of their formation is not fully understood, but they are believed to play a key role in the pathogenesis of cHL.

**Why Each Wrong Option is Incorrect**
**Option A:** While Hodgkin lymphoma can involve any lymph node group, Reed-Sternberg cells are not specific to any particular site.
**Option B:** There are several types of lymphoma, including non-Hodgkin lymphoma (NHL), but Reed-Sternberg cells are characteristic of cHL, not NHL.
**Option C:** While there may be some overlap between the two conditions, Reed-Sternberg cells are not typically seen in lymphoma-like conditions such as Castleman disease.

**Clinical Pearl / High-Yield Fact**
It's essential to distinguish cHL from other types of lymphoma, as the treatment and prognosis differ significantly. Reed-Sternberg cells are a key diagnostic feature, and their presence can guide treatment decisions.

**Correct Answer:** C.