Long-term survival rates in childhood acute lymphoblastic leukemia (ALL) are currently above 85% due to huge improvements in treatment. However, 15-20% of children still experience relapses. Relapses can either occur in the bone marrow or at extramedullary sites, such as gonads or the central nervous system (CNS), formerly referred to as ALL-blast sanctuaries. The reason why ALL cells migrate to and stay in these sites is still unclear. In this review, we have attempted to assemble the evidence concerning the microenvironmental factors that could explain why ALL cells reside in such sites. We present criteria that make extramedullary leukemia niches and solid tumor metastatic niches comparable. Indeed, considering extramedullary leukemias as metastases could be a useful approach for proposing more effective treatments. In this context, we conclude with several examples of potential niche-based therapies which could be successfully added to current treatments of ALL.

Autoimmune pancreatitis (AIP) is rare in teenagers and difficult to diagnose. There are no clear and established diagnostic criteria in the pediatric population to distinguish subtype 1 and subtype 2. Here, we report the case of a 16-year-old white French teenager admitted to the pediatric emergency service with more than 1 year's history of pain originating from the epigastric and the right hypochondriac regions, with bloody diarrhea. After exclusion of pancreatic cancer and other common causes of acute pancreatitis, the diagnosis of AIP was suspected. Biological analyses revealed acute pancreatitis with severe cholestasis and an elevated level of serum immunoglobulin G4. Magnetic resonance cholangiography revealed a voluminous pancreas presenting a typical "sausage-like" aspect. Anatomopathological analyses of the liver biopsy specimen revealed a biliary obstruction due to pancreatic involvement without the typical aspect of chronic destructive cholangitis. Corticotherapy and immunosuppressive treatment proved effective after 1 week of treatment. Without a pancreatic biopsy specimen, the distinction between AIP type 1 and 2 could not be made clearly in this case. The succession of clinical observations could allow clinicians to recognize, treat, and manage AIP in children.

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