Which is the most likely diagnosis for a patient with bleeding gums, bruising, and a peripheral blood smear showing 42% blast forms?

The clinical presentation of the patient, including bleeding gums, bruising, and the peripheral blood smear revealing 42% blast forms, is highly indicative of an acute leukemia. Specifically, the presence of a high percentage of blast cells (which are immature blood cells) signals a rapid accumulation of these cells, a hallmark of acute leukemia.

Acute myelogenous leukemia (AML) typically presents with a higher percentage of myeloid blasts in the peripheral blood or bone marrow, accompanied by symptoms such as bleeding due to thrombocytopenia (low platelet count), anemia, and neutropenia (low white blood cell count). The bleeding gums and easy bruising reported are consistent with the decrease in healthy blood cell production seen in acute leukemia, where normal platelets are often insufficient to maintain hemostasis.

In contrast, acute lymphocytic leukemia (ALL) would also present with similar symptoms and a high proportion of lymphoblastic cells, but the specific details in the question lend themselves more toward the myeloid lineage suggested by the question's context. Chronic leukemias generally present with different clinical manifestations and do not typically show such a high percentage of blasts; they tend to involve more mature cells and exhibit a more gradual progression.

The symptoms and