**Core Concept**
Chronic Lymphocytic Leukemia (CLL) is a type of cancer characterized by the clonal expansion of mature, functionally incompetent lymphocytes. It is primarily a disease of older adults, with a median age of diagnosis in the 70s. CLL is often associated with certain genetic and immunological abnormalities.

**Why the Correct Answer is Right**
CLL is associated with a significant increase in the risk of developing autoimmune disorders, particularly Sjögren's syndrome, rheumatoid arthritis, and autoimmune hemolytic anemia. This is due to the dysfunction of regulatory T cells (Tregs) and the imbalance between pro-inflammatory and anti-inflammatory cytokines. The exact mechanisms underlying the association between CLL and autoimmune diseases are not fully understood, but it is thought to involve the impaired function of Tregs, which normally maintain immune tolerance.

**Why Each Wrong Option is Incorrect**
**Option A:** CLL is not typically associated with a significant increase in the risk of developing gastrointestinal malignancies. While CLL patients may have an increased risk of secondary malignancies, this is not a characteristic feature of the disease.

**Option B:** CLL is not primarily a disease of younger adults. While it can occur at any age, the median age of diagnosis is in the 70s.

**Option C:** CLL is not typically associated with a significant increase in the risk of developing primary central nervous system lymphoma. While lymphoma is a characteristic feature of CLL, primary central nervous system lymphoma is not a common association.

**Clinical Pearl / High-Yield Fact**
CLL patients are at an increased risk of developing autoimmune disorders due to the impaired function of regulatory T cells. This association highlights the importance of monitoring for and managing autoimmune complications in CLL patients.

**Correct Answer:** D.