**Question:** A 17-year-old boy presented with TLC of 138 × 109/L with 80% blasts on the peripheral smear. Chest X-ray demonstrated a large mediastinal mass. Immunophenotyping of this patient's blasts would most likely demonstrate -

A. Lymphoid markers
B. Myeloid markers
C. Both lymphoid and myeloid markers
D. None of the above

**Correct Answer:** **D. None of the above**

**Core Concept:** Acute leukemia

In this scenario, we are discussing a patient with a high number of blasts (80%) in peripheral blood and a large mediastinal mass on chest X-ray, which is highly suggestive of an acute leukemia. Acute leukemia is a group of blood and bone marrow cancers characterized by the rapid proliferation of immature white blood cells (blast cells) in the blood, bone marrow, and sometimes other organs.

**Why the Correct Answer is Right:**

The correct answer is "None of the above" because the blast cells in acute leukemia do not exhibit the typical immunophenotype of lymphoid or myeloid cells. In acute lymphoblastic leukemia (ALL), blast cells express lymphoid markers, while in acute myeloid leukemia (AML), blast cells express myeloid markers or are undifferentiated. In this question, the patient's blast cells exhibit a high percentage of blasts in the peripheral blood and a mediastinal mass, but the immunophenotype is not specified. Therefore, we cannot definitively assign the patient to either ALL or AML category.

**Why Each Wrong Option is Incorrect:**

**A. Lymphoid markers:** While lymphoid markers may be present on blast cells in ALL, the high percentage of blasts and mediastinal mass suggest a different diagnosis.

**B. Myeloid markers:** Similarly, myeloid markers may be present in AML, but the high percentage of blasts and mediastinal mass indicate a different diagnosis.

**C. Both lymphoid and myeloid markers:** The presence of blast cells in the blood and mediastinal mass is more consistent with a leukemia, but the immunophenotype is not specified, so we cannot confirm this diagnosis.

**Clinical Pearls:**

In this case, the presence of blast cells in the blood and mediastinal mass is highly suggestive of acute leukemia. However, without knowledge of the immunophenotype, we cannot definitively assign the patient to either ALL or AML category. This emphasizes the importance of accurate immunophenotyping in differentiating these two subtypes of leukemia.