MIA is elevated in serum from NF1 patients and reflects the internal tumor load. (A) MIA serum levels in 42 NF1 patients and 22 healthy controls. (B) The 42 NF1 patients divided into subgroups according to the absence (-) or presence (+) of pNFs or MPNSTs. (C, D) The 42 NF1 patients were further divided with accordingt to cutaneous and subcutaneous tumors load. (E) In 30 of the 42 NF1 patients, internal tumor load was determined by whole-body magnetic resonance imaging (MRI). The 30 patients were arbitrarily divided into four groups according to the total tumor load: 0 to 100 mL (n = 16), < 350 mL (n = 5), < 1,000 mL (n = 5) and > 1,000 mL (n = 4). Differences between groups were evaluated using an unpaired t-test (A and B) or one-way analysis of variance (ANOVA) with a post hoc t-test including the Bonferroni correction (C to E). **P < 0.01. ***P < 0.001. The linear regression analysis revealed a positive correlation between the logarithm of internal tumor load and MIA serum concentration.