Prognostic significance of Kit receptor tyrosine kinase dysregulations in feline cutaneous mast cell tumors.

Feline cutaneous mast cell tumors (FeCMCTs) are characterized by variable biological behavior. Development of multiple nodules and potential visceral involvement, along with inconsistency of conventional prognostic aids, justify uncertainty in differentiating benign from malignant forms. c-Kit proto-oncogene activating mutations have been reported in feline mast cell tumors (MCTs), but their prognostic relevance was not investigated. This study was performed on FeCMCTs with variable clinical outcome to assess whether Kit cytoplasmic immunohistochemical labeling can be regarded as indicative of c-Kit mutations and to evaluate the relationship between Kit dysregulation and survival. Twenty-four cats diagnosed with a primary cutaneous MCT were enrolled. Kit immunohistochemical pattern and c-Kit (exons 8, 9, 11) mutational status were assessed in 34 tumor samples. Risk factors affecting survival were a number of mitoses greater than 5 per 10 HPFs (P = .017) and cytoplasmic Kit labeling (P = .045). Increased mitotic activity was associated with Kit cytoplasmic expression (P = .01). c-Kit encoding mutations were present in 19 (56%) tumors (exon 8, 19%; exon 9, 71%; exon 11, 10%), however, they were not significantly related to protein expression and they had no influence on prognosis. Additionally, in 6 of 9 (67%) cats, multiple nodules from the same cat had different mutational statuses. Mutations in the fifth immunoglobulin-like domain of Kit occur frequently in FeCMCT, but they are variably associated with aberrant protein expression and do not appear to be strictly correlated with biological behavior. These findings need to be confirmed in larger series, and exploration of further genomic regions of c-Kit is warranted.

Increased serum baseline tryptase levels and extensive skin involvement are predictors for the severity of mast cell activation episodes in children with mastocytosis.

BACKGROUND: Despite the good prognosis of pediatric mastocytosis, some patients suffer from severe mast cell (MC) mediator-associated symptoms. The aim of this study was to identify predictors for severe MC mediator release symptoms in children with mastocytosis in the skin (MIS). METHODS: Serum baseline total tryptase (sbT) levels in 111 children with MIS - 80 maculopapular cutaneous mastocytosis/plaque mastocytosis, 22 nodular mastocytosis, and nine diffuse cutaneous mastocytosis - were investigated as a predictive biomarker for the occurrence of MC mediator-related signs and symptoms within the first 18 months after disease onset. RESULTS: Twelve children (11%) who showed extensive cutaneous disease involving >90% of body surface area (BSA) suffered from severe symptoms requiring hospitalization, with (n = 5) or without (n = 6) management in the intensive care unit (ICU) owing to life-threatening complications. The median sbT was significantly (P < 0.001) higher in patients with extensive cutaneous disease vs those with <90% of BSA involved (45.5 vs 5.2 µg/l, respectively), as well as in children with grade 4 (severe mastocytosis-related symptoms requiring emergency therapy and hospitalization) vs those with grade <4 (46.2 vs 5.2 µg/l, respectively). Receiver operating characteristics curve analyses showed that the optimal cutoff s for sbT to predict the need for daily antimediator therapy, hospitalization, and the management in an ICU were 6.6, 15.5, and 30.8 µg/l, respectively (sensitivity and specificity of 77% and 79%, 100% and 95%, and 100% and 96%, respectively). CONCLUSIONS: Increased sbT in association with extensive cutaneous involvement identifies patients at risk for severe MC activation events in pediatric mastocytosis.

Successful treatment of progressive cutaneous mastocytosis with imatinib in a 2-year-old boy carrying a somatic KIT mutation.

Cutaneous mastocytosis (CM) in children is a usually benign skin disorder caused by mast cell proliferation. Progressive disease leading to systemic involvement and fatal outcomes has been described. C-kit receptor mutations have been identified as causative for CM, some of which potentially respond to imatinib treatment as described for patients with systemic mastocytosis. We report successful therapy of progressive CM with imatinib in a 23-month-old boy. KIT gene analysis revealed not only a somatic deletion of codon 419 in exon 8 (c.1255_1257delGAC) which responds to imatinib therapy, but also a novel germ line p. Ser840Asn substitution encoded by exon 18 in the c-kit kinase domain. Family history suggests this exchange does not affect receptor function or cause disease. Imatinib therapy was well tolerated, stopped symptoms and disease progression, and appeared to shorten the course of the disease. Imatinib could possibly represent a novel therapeutic option in patients with progressive CM.

Serum tryptase and SCORMA (SCORing MAstocytosis) Index as disease severity parameters in childhood and adult cutaneous mastocytosis.

BACKGROUND: Skin lesions are the predominant clinical feature of the commonest form of mastocytosis. Mastocytosis is classified according to World Health Organization criteria. Determination of the levels of mast-cell mediators or their metabolites reflects the mast-cell burden. The extent of cutaneous mastocytosis can be assessed clinically using a scoring system (SCORing MAstocytosis; SCORMA Index) that we have developed. OBJECTIVE: Serum tryptase levels were compared with the SCORMA Index in a large group of paediatric and adult patients to investigate whether there was any correlation between the two. METHODS: The SCORMA Index in 64 patients (31 children and 33 adults) was compared with serum tryptase levels. The results of the first visit at which SCORMA and tryptase were evaluated were analysed. RESULTS: There was a positive correlation between the SCORMA Index and serum tryptase levels, indicating the value of the SCORMA Index in the assessment of mastocytosis with skin involvement. CONCLUSION: The results of this study showed that the SCORMA Index is a useful tool for evaluating the severity of cutaneous mastocytosis. The correlation between the SCORMA Index and serum tryptase levels underlines the benefit of the SCORMA Index as a clinical tool. Repeated SCORMA Index measurements can provide a rapid impression of changes in the clinical state of mastocytosis. This is particularly relevant in children, because taking blood samples from this group is much more difficult. The well-established methods for evaluation of disease severity may be expanded by the rapid SCORMA Index method.

Immune response against HtrA proteases in children with cutaneous mastocytosis.

Mast cells play an important role in both, the innate and adaptive immunity, however, clonal proliferation of abnormal mast cells in various organs leads to mastocytosis. A skin variant of the disease, cutaneous mastocytosis (CM) is the most frequent form of mastocytosis in children. HtrA proteases are modulators of important cellular processes, including cell signaling and apoptosis, and are related to development of several pathologies. The above and the observation that mast cells constitutively release the HtrA1 protein, prompted us to investigate a possible involvement of the HtrA proteins in pediatric CM. Levels of the serum autoantibodies (IgG) against the recombinant HtrA proteins (HtrA1-4) in children with CM (n=36) and in healthy controls (n=62) were assayed. Anti-HtrA IgGs were detected using enzyme linked immunosorbent assay (ELISA) and Western-blotting. In the CM sera, levels of the anti-HtrA1 and anti-HtrA3 autoantibodies were significantly increased when compared to the control group, while the HtrA protein levels were comparable. No significant differences in the anti-HtrA2 IgG level were found; for the anti-HtrA4 IgGs lower levels in CM group were revealed. In healthy children, the IgG levels against the HtrA1, -3 and -4 increased significantly with the age of children; no significant changes were observed for the anti-HtrA2 IgG. Our results suggest involvement of the HtrA1 and HtrA3 proteins in pediatric CM; involvement of the HtrA4 protein is possible but needs to be investigated further. In healthy children, the autoantibody levels against HtrA1, -3 and -4, but not against HtrA2, increase with age.

Tryptase haplotype in mastocytosis: relationship to disease variant and diagnostic utility of total tryptase levels.

Serum mast cell tryptase levels are used as a diagnostic criterion and surrogate marker of disease severity in mastocytosis. Approximately 29% of the healthy population lacks alpha tryptase genes; however, it is not known whether lack of alpha tryptase genes leads to variability in tryptase levels or impacts on disease severity in mastocytosis. We have thus analyzed tryptase haplotype in patients with mastocytosis, computing correlations between haplotype and plasma total and mature tryptase levels; and disease category. We found: (1) the distribution of tryptase haplotype in patients with mastocytosis appeared consistent with Hardy-Weinberg equilibrium and the distribution in the general population; (2) the disease severity and plasma tryptase levels were not affected by the number of alpha or beta tryptase alleles in this study; and (3) information about the tryptase haplotype did not provide any prognostic value about the severity of disease. Total and mature tryptase levels positively correlated with disease severity, as well as prothrombin time and partial thromboplastin time, and negatively correlated with the hemoglobin concentration.

Detection of phospho-STAT5 in mast cells: a reliable phenotypic marker of systemic mast cell disease that reflects constitutive tyrosine kinase activation.

Systemic mastocytosis (SM) is characterized by the abnormal proliferation and accumulation of mast cells (MCs). Constitutive activation of kit, a receptor tyrosine kinase (TK), has been associated with all types of SM. Signal transducers and activators of transcription (STATs), such as STAT5, mediate downstream kit signalling. We hypothesized that nuclear phospho-STAT5 (pSTAT5) in MCs might reflect TK activation and would be a marker of abnormal MCs in SM. Expression of tryptase, CD25, CD2 and pSTAT5 was evaluated by immunohistochemistry (IHC) on archival cases of SM and cutaneous mastocytosis (CM). pSTAT5 was detected in 23/23 of SM and 1/9 of CM MC nuclei. 23/23 SM had CD25 + MCs. Control tissue MCs were negative for pSTAT5. Nuclear pSTAT5 in MCs from SM reflects abnormal TK activation. We propose nuclear pSTAT5 positivity in MCs as an additional minor phenotypic criterion for diagnosis of SM in future World Health Organization classification schemes.