Minimal Disseminated Disease (MDD) in BM of Childhood T-Cell Lymphoblastic Lymphoma (Stage III), Detected by Flow Cytometry (FC) and Real Time Quantitative Polymerase Chain Reaction (RQ-PCR).

Despite overlapping features between T cell Lymphoma and T cell ALL and generally good response to T-ALL type of treatment there are some clinical and biological differences between the two entities. The aim of this study was to evaluate in children with stage III T cell Lymphoma the prevalence of minimal BM dissemination at diagnosis, its prognostic significance and early response kinetics. Bone Marrow (BM) at diagnosis from 14 children with T- cell lymphoblastic lymphoma (T-LBL) was assessed for minimal disseminated disease (MDD) by flow cytometry (FC) with four colour antibody combinations and real time quantitative PCR (RQ-PCR) with specific junctional regions for T-cell receptor and immunoglobulin heavy chain gene rearrangements. 13 pts. had stage III mediastinal lymphoma, and one stage II cervical disease. Morphological BM involvement of almost 5% blasts was suspected in only one patient. All, but one, were treated according to the NHL-BFM 90/95 protocols medium risk group (without irradiation). In addition, 7 pts were assessed for early response on week 5 and 12 of treatment with PCR only (2 pts) FC only (2 pts) and both methods (3 pts). Lymphoma associated immunophenotype with a sensitivity of at least 0.01% was detected in all patients (100%) (2 combinations), and PCR targets with a sensitivity of 0.01% and 0.1% in 10 and 2 examined patients respectively (92%). A sample with a level of above 5X10⁻⁴ was considered as positive MDD or minimal residual disease (MRD) by both methods. By FC, 10 patients exhibited positive and 4 negative BM MDD levels at diagnosis. By RQ -PCR, 7 patients presented positive and 4 negative BM MDD levels. Both methods gave consistent results with only one case of discordance: negative in PCR and positive in FC (>5x10⁻⁴). In 7 other pts there was a difference of between 0.5 and 1 log level that did not change the classification of involvement (in 5 pts PCR higher, in 2 pts FC higher). At a median follow up of 5 years, 3 patients relapsed (2 in the mediastinum and one in BM) their MDD level at diagnosis was 2x10⁻³ (2 pts), 6x10⁻². MRD level in 4 patients out of 5 patients with a high MDD level (1–6x10⁻²) at diagnosis, decreased by 2 logs (<5x10⁻⁴) on week 5, and on week 12 all were below <2x10⁻⁴. The one patient with a higher level (1.5x10⁻²) at day 33 suffered a relapse.

In conclusion: in the majority of patients with mediastinal stage III T-cell lymphoma molecular BM dissemination (>5x10⁻⁴) was present. It’s prognostic significance in the context of ALL-BFM therapy could not be demonstrated. However, early BM molecular treatment response in T-cell Lymphoma may correlate with outcome, similarly to T-cell leukemia.