**Core Concept**
Lymphomas are a diverse group of malignancies arising from lymphoid cells, including B cells, T cells, and natural killer (NK) cells. They can be broadly classified into Hodgkin lymphoma (HL) and non-Hodgkin lymphoma (NHL), each with distinct clinical and pathological features.

**Why the Correct Answer is Right**
The correct answer is related to the pathophysiology and classification of lymphomas. Lymphomas are characterized by abnormal proliferation of lymphoid cells, which can lead to the formation of lymphoid tissues in various organs, including lymph nodes, spleen, and bone marrow. The distinction between HL and NHL is crucial for diagnosis and treatment planning.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because lymphomas are not typically associated with increased levels of immunoglobulins (Ig) in the serum. While some lymphomas may produce monoclonal proteins, this is not a universal feature of all lymphomas.
**Option B:** This option is incorrect because lymphomas can indeed involve the central nervous system (CNS), leading to symptoms such as headache, seizures, or cognitive impairment.
**Option C:** This option is incorrect because lymphomas can be sensitive to radiation therapy, which is often used as part of the treatment regimen.

**Clinical Pearl / High-Yield Fact**
It's essential to note that lymphomas can present with a wide range of symptoms, including fever, weight loss, and fatigue. A thorough history and physical examination, combined with diagnostic imaging and biopsy, are crucial for accurate diagnosis and staging of lymphoma.

**Correct Answer: A.**