Mastocytosis: review of clinical and experimental aspects

Therapeutic modulation of KIT ligand in melanocytic disorders with implications for mast cell diseases

KIT ligand and its associated receptor KIT serve as a master regulatory system for both melanocytes and mast cells controlling survival, migration, proliferation and activation. Blockade of this pathway results in cell depletion, while overactivation leads to mastocytosis or melanoma. Expression defects are associated with pigmentary and mast cell disorders. KIT ligand regulation is complex but efficient targeting of this system would be of significant benefit to those suffering from melanocytic or mast cell disorders. Herein, we review the known associations of this pathway with cutaneous diseases and the regulators of this system both in skin and in the more well-studied germ cell system. Exogenous agents modulating this pathway will also be presented. Ultimately, we will review potential therapeutic opportunities to help our patients with melanocytic and mast cell disease processes potentially including vitiligo, hair greying, melasma, urticaria, mastocytosis and melanoma.

Intracellular Noise Level Determines Ratio Control Strategy Confined by Speed-Accuracy Trade-off

Robust and precise ratio control of heterogeneous phenotypes within an isogenic population is an essential task, especially in the development and differentiation of a large number of cells such as bacteria, sensory receptors, and blood cells. However, the mechanisms of such ratio control are poorly understood. Here, we employ experimental and mathematical techniques to understand the combined effects of signal induction and gene expression stochasticity on phenotypic multimodality. We identify two strategies to control phenotypic ratios from an initially homogeneous population, suitable roughly to high-noise and low-noise intracellular environments, and we show that both can be used to generate precise fractional differentiation. In noisy gene expression contexts, such as those found in bacteria, induction within the circuit's bistable region is enough to cause noise-induced bimodality within a feasible time frame. However, in less noisy contexts, such as tightly controlled eukaryotic systems, spontaneous state transitions are rare and hence bimodality needs to be induced with a controlled pulse of induction that falls outside the bistable region. Finally, we show that noise levels, system response time, and ratio tuning accuracy impose trade-offs and limitations on both ratio control strategies, which guide the selection of strategy alternatives.

Two cases of mimics of bone metastasis in breast cancer

In patients with breast cancer, the appearance of sclerotic bone lesions on imaging should raise the suspicion of skeletal metastases. However, before making the diagnosis it is important to consider the clinical context and remember that there are conditions that can mimic bone metastasis. We present two cases of mimics of bone metastasis: systemic mastocytosis and osteopoikilosis. These cases demonstrate clinical and radiological characteristics that would make a diagnosis of bone metastasis less likely, and highlight the need for an awareness of mimics of bone metastasis.

Successful Treatment of Provisional Cutaneous Mastocytosis with Interferon Alpha

Mastocytosis is a disorder characterized by the clonal proliferation of mast cells and their accumulation in skin, bone marrow, liver, and spleen. Cutaneous mastocytosis presents in children in over 90% of the cases and any cutaneous manifestation in an adult is the earliest sign of the systemic disease. A 45-year-old patient presented with itchy dark lesions over the body since childhood and Darier's sign was positive. Skin biopsy showed features of mastocytosis and immunohistochemistry was positive for CD34. Since the patient was refractory to treatment with antihistamines and psoralen-ultraviolet A therapy, injections of interferon alpha were given – 3 million IU twice weekly subcutaneously as they have been proven to improve constitutional symptoms. Very few reports of successful treatment of cutaneous mastocytosis using interferon alpha have been published.

Aspirin in dermatology: Revisited

Aspirin has been one of the oldest drugs in the field of medicine, with a wide range of applications. In dermatology, aspirin has shown benefit in a variety of disorders. Recently, reduction of melanoma risk with aspirin has been demonstrated. Although an analgesic to begin with, aspirin has come a long way; after cardiology, it is now found to be useful even in dermatology.

A 1-year-old boy with persistent, generalized eruption. Urticaria pigmentosa

A healthy 1-year-old boy born at full term after an uncomplicated pregnancy presented to the dermatology clinic for a widespread eruption with gradual onset since 3 months of age. He was otherwise well, afebrile, feeding well, and gaining weight appropriately. The child was overall asymptomatic, though some of his lesions occasionally became red and pruritic. His mother noticed that after mild illnesses, he was more prone to these flares. She denied flushing, vomiting, diarrhea, respiratory distress, and irritability. He was meeting all developmental milestones and started walking at 11 months of age. The remainder of his review of systems was unremarkable, and family history was noncontributory. Physical exam revealed a well-appearing, well-nourished, playful, and interactive toddler. There were innumerable discrete and coalescing pink-brown macules and papules concentrated on the trunk and extending onto the proximal upper and lower extremities bilaterally, as well as the neck and lower face. Stroking the lesions quickly led to development of erythematous edematous wheals. There was no hepatosplenomegaly, and the lymph node exam was unremarkable.

Identification of KIT activating mutations in paediatric solitary mastocytoma

AIMS

Mastocytosis is an abnormal mast cell proliferation involving one or more organs, in particular the skin and bone marrow. In children, disease is usually limited to the skin, with three distinct clinical presentations: urticaria pigmentosa, diffuse cutaneous mastocytosis and solitary mastocytoma. Although the KIT D816V mutation is typically found in adult-onset mastocytosis, it is less commonly seen in childhood-onset mastocytosis, and the frequency of KIT mutations in paediatric solitary mastocytoma is poorly documented.

METHODS AND RESULTS

In this study we analysed KIT exons 8, 9, 11, 13 and 17 in nine cases of paediatric solitary mastocytoma using a laboratory-developed Sanger sequencing assay. A KIT mutation was identified in six cases (67%), including three with the D816V mutation typical of adult-onset disease, and another three with an internal tandem duplication (p.A502_Y503dup) in exon 9, previously described in gastrointestinal stromal tumour.

CONCLUSIONS

Paediatric solitary mastocytoma is frequently associated with KIT activating mutations, in keeping with a clonal process. KIT mutational status appears insufficient to explain the divergent biology of childhood and adult-onset disease.

Comparative study of systemic psoralen and ultraviolet A and narrowband ultraviolet B in treatment of chronic urticaria

BACKGROUND

Previous success rates of psoralen and ultraviolet A (PUVA) and narrowband UVB (NB-UVB) in the treatment of chronic urticaria are reported in few studies with no previous reports on the comparable efficacy of both modalities in the disease.

AIM

We aimed to compare the efficacy of PUVA versus NB-UVB in the treatment of chronic urticaria.

METHODS

Twenty-four patients with chronic urticaria were included and divided into two groups: 12 patients subjected to PUVA and 12 subjected to NB-UVB. They were compared according to the urticaria Total Severity Score (TSS) before and after treatment, cumulative dose, and side effects.

RESULTS

There was a statistically significant decrease in urticaria TSS in both the NB-UVB- and PUVA-treated groups after than before treatment (P < 0.05), with no significant difference between both groups regarding the percentage of improved patients and the mean decrease of urticaria TSS (P > 0.05). Gastrointestinal upset was reported at a significantly higher percentage in the PUVA-treated group than in the NB-UVB-treated group.

CONCLUSION

Both NB-UVB and PUVA show comparable efficacy in the treatment of chronic urticaria with minimal reversible side effects.

Polycythemia from mast cell activation syndrome: lessons learned

A middle-aged woman presented with fatigue and mild increases in hematocrit and red cell mass. Polycythemia vera was diagnosed. She underwent therapeutic phlebotomy but clinically worsened. On reevaluation, other problems were noted including episodic malaise, nausea, rash and vasomotor issues. The JAK2V617F mutation was absent; paraneoplastic erythrocytosis was investigated. Serum tryptase and urinary N-methylhistamine were normal, but urinary prostaglandin D2 was elevated. Skin and marrow biopsies showed no mast cell abnormalities. Extensive other evaluation was negative. Gastrointestinal tract biopsies were histologically normal but revealed increased, aberrant mast cells on immunohistochemistry; the KITD816V mutation was absent. Mast cell activation syndrome, recently identified as a clonal disorder involving assorted KIT mutations, was diagnosed. Imatinib 200 mg/d rapidly effected complete, sustained response. Diagnosis of mast cell activation syndrome is hindered by multiple factors, but existing therapies for mast cell disease are usually achieve significant benefit, highlighting the importance of early diagnosis. Multiple important aspects of clinical reasoning are illustrated by the case.

Merkel cell carcinoma: evaluation of KIT (CD117) expression and failure to demonstrate activating mutations in the C-KIT proto-oncogene ? implications for treatment with imatinib mesylate

BACKGROUND

Merkel cell carcinomas (MCCs) express the tyrosine kinase receptor KIT. However, it is not known if MCCs have activating mutations in KIT that would make them responsive to treatment with imatinib mesylate. The purpose of this article is to describe the KIT immunohistological staining pattern (CD117) of MCCs and analyze those MCCs for mutations in areas of KIT where mutations are found in gastrointestinal stromal cell tumors.

METHODS

We evaluated KIT immunostaining in nine MCCs from nine patients. In addition, we extracted DNA from the same MCCs, performed PCR amplification of C-KIT exons 9, 11, 13, and 17, and sequenced those gene products for mutations.

RESULTS

Eight of nine (88.8%) MCCs expressed KIT. No mutations were found.

CONCLUSIONS

The majority of MCCs express KIT but do not contain activating mutations in exons 9, 11, 13, or 17 of KIT. Imatinib mesylate is unlikely to provide effective therapy in MCC unless activating mutations in other areas of KIT or activating mutations in other related genes can be detected.

Mast cells in photodamaged skin: what is their role in skin cancer?

In this review, changes that we have observed in the prevalence of mast cells in human sun-exposed skin, and their potential immunoregulatory role, are discussed. More specifically, in a study of Australian volunteers, the prevalence of dermal mast cells was increased in back-of-hand skin, anecdotally the most sun-exposed site of the body, but not in skin from buttock, inner arm or shoulder. By histological analysis of back-of-hand skin, there was a significant correlation between dermal mast cell prevalence and elastin content suggesting increased mast cell prevalence with photodamage. We hypothesised that these mast cells were immunomodulatory upon activation by sun exposure. However, no link was found between dermal mast cell prevalence in hand skin and the presence of basal cell carcinomas. Finally, we discuss other roles for increased numbers of mast cells in UV-exposed photodamaged skin.

Bivalent effect of UV light on human skin mast cells-low-level mediator release at baseline but potent suppression upon mast cell triggering

Ultraviolet (UV) irradiation is an established treatment for inflammatory skin diseases, although the precise mode of action is still unclear. Activating and suppressive effects on mast cell (MC) mediator release have been described. The aim of this study was to investigate systematically the effects of UVB, UVA-1, and psoralen plus UVA-1 at therapeutic doses on skin-derived human MC. Baseline and stimulated release of histamine, tryptase, and of interleukin (IL)-6, IL-8 and tumor necrosis factor-alpha (TNF-alpha) were examined. In resting MC, UV light induced a slight, yet significant histamine release corresponding to enhanced surface levels of lysosome-associated membrane proteins (LAMP). In contrast, UV pre-treatment caused a marked suppression of the anti-IgE-induced histamine release, accompanied by a diminished, anti-IgE-mediated increase in LAMP expression. The secretion of IL-6, IL-8, and TNF-alpha was inhibited in resting and activated MC, suggesting a different mode of action. Regarding the importance of MC in a variety of allergic and inflammatory processes, our data show a high susceptibility of this cell type towards UV light, which seems to partially depend on the state of cellular activation. Immunosuppressive effects predominate in activated MC, thus corresponding with the beneficial effects in inflammatory diseases, whereas in resting MC, both stimulatory and inhibitory effects are observed.

Mast cells and the inflammatory response to different implanted biomaterials

The biocompatibility of dental materials is a topic of increasing importance for dentists. We investigated the effects of alloys for ceramic crowns and removable prostheses on the skin and lymphoid organs of rats. We used three groups of Sprague Dawley rats: group I as the control, with groups II and III implanted with different biomaterials into subcutaneous pockets. After sacrifice, the rat skin around the implant and the lymph nodes was studied. The tissues of implanted rats were morphologically different from the control animals as they showed a number of mast cells that increased 7 days after the implant with both alloys. These cells decreased 14 days after the implant with alloy for ceramic crowns whereas they were still high 28 days after the implant with alloy for removable prostheses. The findings suggest that both alloys induced different and time-dependent inflammatory reactions. Our findings have importance in the future rational design of biocompatible implantable and blood-contact biomaterials.

CD117 (KIT receptor) expression in Merkel cell carcinoma

The KIT receptor tyrosine kinase (CD117 antigen) is found in a variety of normal tissue cell types and in several malignant tumors, including acute myeloid leukemia. We recently encountered two tumors initially suspected as acute myeloid leukemia cutis and expressing CD117 that showed punctate positivity for cytokeratin 20 diagnostic for Merkel cell carcinoma. We evaluated 20 additional cases of MCC and found that 21 of 22 tumors (95%) expressed CD117. Intensity of CD117 expression did not appear to correlate with aggressive behavior. While the function of the KIT receptor in MCC is not known, its pathogenic role in other malignant neoplasms suggests the possibility of a similar role in MCC.