This study consists of 25 patients with chronic granulocytic leukemia in blast crisis (BC) or with acute leukemia who had a Ph' chromosome and one or more other chromosome abnormalities and who were investigated by cytochemistry and immunocytochemistry techniques to determine whether the predominant blasts were myeloid or lymphoid. The disorder was myeloid in 15 patients, lymphoid in 8, and mixed in 2. Among the 15 patients with myeioid disorders, 13 (86.6%) had an additional Ph'chromosome, i(17q), + 8, + 19, or some comblnation of these abnormailties. None of the elght patients with a lymphoid disorder had + 8, + 19, or 1(17q), but one had an additional Ph' chromosome.
Among the elght patients with lymphoid disorders, two had structural abnormalities of chromosome 7 and two were monosomy 7. None of the patients with myeioid disease had a structurally abnormal chromosome 7, but one was monosomy 7. Our findings suggest that the number of chromosomes in an abnormal clone may be unreliable for distinguishing between lymphoid and myeioid BC. Most patients with myeloid disease had only abnormal metaphases, whereas many patients with lymphoid disorders had both normal and abnormal metaphases. This finding may partially explain why many patients with lymphoid BC respond better to treatment than do those with myeioid BC.