## Core Concept
Chloroma, also known as granulocytic sarcoma, is a rare extramedullary tumor composed of immature granulocytic cells. It is associated with acute myeloid leukemia (AML) and other myeloproliferative disorders. The condition represents a localized proliferation of leukemic cells.

## Why the Correct Answer is Right
The correct answer, **C. Myeloid lineage leukemic cells**, is right because chloroma is specifically composed of immature myeloid cells, which are the cells that give rise to granulocytes (a type of white blood cell). These cells are typically seen in conditions like acute myeloid leukemia (AML), where there is an abnormal proliferation of myeloid cells. The presence of chloroma indicates the extramedullary involvement of these leukemic cells.

## Why Each Wrong Option is Incorrect
- **Option A:** Lymphoid cells - This option is incorrect because chloroma is specifically associated with myeloid lineage cells, not lymphoid cells. Lymphoid cells are involved in different types of leukemia, such as acute lymphoblastic leukemia (ALL).
- **Option B:** Mature granulocytic cells - This option is incorrect because chloroma consists of immature granulocytic cells, not mature ones. Mature granulocytic cells are typically found in the peripheral blood and are not associated with the formation of chloromas.
- **Option D:** Blast cells of lymphoid lineage - This option is incorrect for similar reasons as Option A; chloroma is associated with myeloid lineage cells, not lymphoid blast cells.

## Clinical Pearl / High-Yield Fact
A key clinical pearl is that chloroma often presents as a greenish mass (due to the presence of myeloperoxidase) and can occur in various sites, including the skin, soft tissues, lymph nodes, and bones. Recognizing chloroma is crucial because it can be a presenting feature of acute myeloid leukemia and signifies a poor prognosis.

## Correct Answer: C. Myeloid lineage leukemic cells