A European Society for Medical Oncology (ESMO)-sponsored expert meeting was held in Paris on 8 March 2018 which comprised 11 experts from academia, 11 experts from the pharmaceutical industry and 2 clinicians who were representatives of ESMO. The focus of the meeting was exclusively on the intratumoral injection/delivery of immunostimulatory agents with the aim of harmonizing the standard terms and methodologies used in the reporting of human intratumoral immunotherapy (HIT-IT) clinical trials to ensure quality assurance and avoid a blurring of the data reported from different studies. The goal was to provide a reference document, endorsed by the panel members that could provide guidance to clinical investigators, pharmaceutical companies, ethics committees, independent review boards, patient advocates and the regulatory authorities and promote an increase in the number and quality of HIT-IT clinical trials in the future. Particular emphasis was placed not only on the development of precise definitions to facilitate a better understanding between investigators but also on the importance of systematic serial biopsies as a driver for translational research and the need for the recording and reporting of data, to facilitate a better understanding of the key processes involved.

Cellular drug resistance is thought to be an important cause of the poor prognosis for children with relapsed or refractory acute lymphoblastic leukemia (ALL), but it is unknown when, to which drugs, and to what extent resistance is present. We determined in vitro resistance to 13 drugs with the MlT assay. Compared with 141 children with initial ALL, cells from 137 children with relapsed ALL were significantly more resistant to glucocorticoids, L-asparaginase, anthracyclines, and thiopurines, but not to vinca-alkaloids, cytarabine, ifosfamide, and epipodophyllotoxins. Relapsed ALL cells expressed the highest level of resistance to glucocorticoids, with a median level 357-and >24-fold more resistant to prednisolone and dexamethasone, respectively, than ini-OWADAYS, using intensive front-line multiagent chemotherapy along with improved supportive care, more than 95% of children with acute lymphoblastic leukemia (ALL) can achieve a complete remission (CR), of whom 70% will remain in continuous CR and be considered cured.'-3 These results show the tremendous improvement in the development of more effective chemotherapy regimens for childhood ALL, which was once a fatal d i~e a s e .~ Nevertheless, current protocols fail in the remaining 30% of the children with newly diagnosed ALL, with bone marrow relapses representing the most common treatment failures.'-3 Second remissions can be induced with intensified chemotherapy in more than 90% of the children with ALL whose disease relapsed while they were on modem protocols, but their long-term prognosis is p~o r . ' .~.~ Long-lasting second hematologic remissions can be expected in about 10% of the children with early relapses and in up to 30% of those with late relapses, despite even more intensive second-line therapy that includes the effective front-line drugs used in an alternative Knowledge about the nature of relapsed ALL is limited, but it is assumed that regrowth of drug-resistant leukemic cells plays an important role.6 It is unknown to which drugs and to what extent relapsed leukemic cells express resistance, mainly because a suitable drug-resistance assay was lacking until recently. The poor growth capacity of ALL cells in vitro, limiting the use of long-term clonogenic assays, could be circumvented with the introduction of so-called shortterm cell culture drug-resistance assay^.^ The 3-[4,5-dimethyl-thiazol-2,5-diphenyl] tetrazolium bromide (MTT) assay, first described by Black and Speer in 1954' and revised by Mosmann in 1983: has been adapted by us for testing ALL cells."." The 4-day semiautomated MTT assay is an efficient tool for large-scale drug-resistance testing and results showed a good correlation with the prognosis in childhood We present here the results of in vitro drugresistance testing on samples from 141 children with relapsed or refractory ALL.

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Glucocorticoids (GC) are being used in the treatment of childhood leukemia for several decades, most successfully in newly diagnosed acute lymphoblastic leukemia (ALL). However, GC resistance is seen in 10-30% of untreated ALL patients, and is much more frequent in relapsed ALL and in acute nonlymphoblastic leukemia (ANLL). Sensitivity or resistance to GC can be measured using a cell culture drug resistance assay. For this purpose, we use the colorimetric methyl-thiazol-tetrazolium (MTT) assay. We have shown that GC resistance in childhood leukemia is related to clinical and cell biological features, and to the clinical outcome after multi-drug chemotherapy. These results are summarized in this review. In addition, we describe the apoptotic 'cell-lysis pathway' by which GC exert their antileukemic activity. This description provides a model to discuss the mechanisms of GC resistance, and to summarize the relevant literature. Possible levels of resistance relate to the diffusion of GC through the cell membrane, binding to the GC receptor (GCR), activation of the GC-GCR complex, translocation of the complex into the nucleus, binding to DNA, endonuclease-mediated DNA fragmentation, and DNA repair. A low number of GCR has been shown to be the cause of resistance in some children with ALL. However, GC resistance is likely to be caused at the post-receptor level in most leukemias. Unfortunately, there is still a lack of knowledge relating to the clinical relevance of mechanisms of GC resistance at the post-receptor level. Studies on the mechanisms of GC resistance other than those directly related to the GCR should be initiated, especially if patient material is used, as the results might indicate ways to circumvent or modulate GC resistance. A further increase in our knowledge regarding the relation between GC resistance and patient and cell biological features, the clinical relevance of GC resistance, and the mechanisms of GC resistance in leukemia patients, may contribute to further improvement in the results of GC therapy in leukemia.

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