Background: Lymphoblastic lymphomas (LL) of the mediastinum are rare tumours that present a challenging diagnosis. The positive diagnosis is based on microscopic findings. Our aim was to highlight the diagnostic difficulties in such situations. Methods: We conducted a descriptive retrospective study including 31 patients presenting mediastinal LL. Results: Radiologic features consisted in all cases in a mediastinal infiltrating mass. Microscopic examination showed in all cases a crowded tumour with many artefacts made of diffuse tumour cells. Immunohistochemial study was performed in all cases. It was quite difficult to interprete in the samples used for extemporaneous examination and repeated in 10 cases. Conclusion: The diagnosis of LL is based on the microscopic examination which is usually performed on small samples with crowding artefacts. Thus, this pathology must be managed by a trained team that is used to deal with such a specimen in order to avoid repeating the biopsy and inducing diagnostic delay.

Dear Editor,Lymphoblastic lymphoma (LL) of the mediastinum is a rare tumour accounting for 2 % of non-Hodgkin lymphomas. It is a diagnostic and therapeutic emergency. Positive diagnosis is based on microscopic examination. They are classified as T LL in 85 to 90 % of the cases. Few survival studies have been reported, and our knowledge about these tumours is based on rare case reports and case studies [1]. Our aim was to assess the most relevant factors influencing the survival of patients presenting mediastinal LL.We conducted a retrospective single-centre study over a 16-year period between 2000 and 2015 including all patients presenting mediastinal LL. Patients with other mediastinal lesions were ruled out. Two age groups were identified: the pediatric age lower than 15 years and the adult age superior to 15 years. The tumours were subdivided into localized tumours including stages I and II according to the Ann Arbor classification of lymphoma and disseminated tumours including stages III and IVaccording to the same classification. The nature of the specimen, the gross exam, the microscopic features and the crowding artefacts were recorded. The immunohistochemical study was performed in all cases using a manual method performed by the same technician. The different antibodies included CD3, CD5, CD99, CD1a, CD45, Tdt, Ki-67, CD20, CK, EMA, CD79a, CD15 and CD30 antibodies. A multivariate analysis was performed to compare the sex, the gender and the age in relation to the global survival of the patients using cox model. The SPSS software (version 15.0) was used.Thirty-one T cell LL of the mediastinum were diagnosed. The mean age of the patients was 26 years. A male predominance was noticed with 19 men and 12 women. The global survival was estimated to 85 % at 8 months and 70 % at 12 months with a mean survival of 24 months. The multivariate analysis revealed that the sex was a relevant prognostic factor (p = 0.045). Table 1 illustrates the different results related to the odds ratio, the confidence interval and the p values.This study highlights the bad prognosis of these tumours with a global survival of 24 months versus 43 months in the literature. Many prognostic factors have been reported in the literature [2,3]. The young age is considered as a prognostic factor [4,5]. This was not proved in our study (p = 0.46). The female sex is considered as a prognostic factor either in our study or in the literature review (p = 0.045) [6]. In opposition to the literature, the stage does not seem to play a key role (p = 0.88) [7].Other prognostic factors have been reported in the literature including mir17, mir 19, MYC, bcl2, bcl6 and the c-myc without a real consensus [8,9].Our survival study revealed the prognostic relevance of the gender in LL. The prognostic impact of the subtype of the lymphoma was not highlighted because all the cases diagnosed were of T cell subtype. This fact is concordant to the literature review because the majority of mediastinal LL are of T cell subtype.