Myeloid sarcoma. Light micrograph of a diffuse infiltrate of medium to large mononuclear cells surrounding the ductal elements with effacement of normal architecture. Myeloid sarcoma rarely involves the breast, even though breast and testis are the two most commonly reported sites for acute myeloid leukaemia (AML) relapse. The mere presence of a leukemic infiltrate in the breast does not qualify for the diagnosis of myeloid sarcoma. There needs to be effacement of tissue architecture. Most patients are premenopausal (below age 50).