Helical tomotherapy and systemic targeted therapies in solitary plasmacytoma: Pilot study

To assess the feasibility of the combination of helical tomotherapy(®) (HT) and a concurrent systemic targeted therapy in patients with solitary plasmacytoma (SP) with the aim to decrease toxicity while improving therapeutic efficacy.

Six patients with biologically, histologically, and radiologically confirmed SP were treated using HT and a systemic targeted treatment concomitantly. Total dose was 40 Gy/20 fractions. Four patients received 4 cycles of concurrent lenalidomide-dexamethasone combination and two patients were treated with concomitant bortezomib-dexamethasone. All toxicities were described using the Common Terminology Criteria for Adverse Effects v3.0.

Five patients had a bone tumor and one patient had an isolated pancreatic mass. Five patients presented with pain, one had neurologic symptoms related to medullary compression, which was treated by an emergency surgery. Median age was 59.5 years (range, 50-74 years). All patients had initial positron emission tomography-computed tomographys, three patients had total body bone magnetic resonance imaging examination, and three patients had computed tomodensitometry scans. The toxicity profile was excellent with no higher than grade 1 toxicity. Four of the six patients experienced a partial radiological response, four had complete response on positions emission tomography and 5/6 patients experienced a complete relief of their symptoms 4 mo after treatment. At a median follow-up of 18 mo, 5/6 patients were controlled clinically, radiologically, and biologically.

Using HT, we could deliver a highly conformal irradiation concurrently with a molecularly targeted therapy. This association yielded in a high response rate and a low toxicity. A prospective study with longer follow-up will help determining the true benefit of such strategy.