Gallium-67 imaging: a predictor of residual tumor viability and clinical outcome in patients with diffuse large-cell lymphoma.

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Abstract
Durable complete remissions (CRs) can be achieved in patients with diffuse large-cell lymphoma (DLCL) with multidrug chemotherapy. The length of time to reach CR may be predictive of treatment outcome. However, defining CR by chest radiograph or computed tomography (CT) is often difficult since residual abnormalities do not always indicate residual disease. We have prospectively evaluated the ability of gallium-67 citrate (Ga-67) imaging to define residual disease and predict outcome in 37 consecutive patients with DLCL. Patients received 296 to 370 megabecquerels (MBq) Ga-67 and were imaged prior to, following cycles 4 to 6, and at completion of intensive chemotherapy. Ga-67 scan results were correlated with radiographic studies. Seventeen of 37 patients (46%) showed persistent, abnormal Ga-67 uptake halfway through chemotherapy. Of these, four were in CR, 11 were in partial remission (PR), and two showed no change in tumor size. At follow-up, 10 (59%) have died (three who were scored as CR and seven who were in PR halfway through therapy), two are alive with active tumor, one relapsed and survives following bone marrow transplant, and four (three in PR and one in CR at the therapeutic halfway point) are without disease at a median of 28 months from presentation. Of the 20 patients who were Ga-67-negative halfway through therapy, 11 were in CR and nine were in PR. Five of 20 patients (25%) have died. Three, in radiographic CR died at 11, 26, and 28 months, and two in radiographic PR died at 15 and 17 months. One patient is alive with active tumor, and 14 patients (70%) are alive without disease at a median of 34 months from presentation. Ga-67 imaging proved to be an excellent indicator of residual viable tumor; a positive scan halfway through therapy predicted for a poor outcome and may well justify a change in treatment.