Continuing Education Activity

This continuing medical education activity reviews the evaluation and treatment of cutaneous mastocytosis and mastocytoma, with emphasis on distinguishing localized pediatric disease from systemic mastocytosis and other conditions that can mimic mast cell mediator symptoms. Mastocytosis may present with pigmented macules, papules, nodules, pruritus, flushing, blistering, gastrointestinal tract symptoms, syncope, or anaphylaxis, requiring careful clinical assessment and appropriate use of histology, serum tryptase levels, complete blood cell count, molecular testing, and imaging when systemic involvement is suspected. The practice gap is inconsistent recognition of diagnostic criteria, risk features, and indications for additional evaluation, which can lead to delayed diagnosis, unnecessary testing, missed systemic disease, or inadequate anaphylaxis prevention. This activity addresses that gap by strengthening diagnostic reasoning, evidence-based symptomatic treatment, trigger avoidance counseling, epinephrine education, and interprofessional collaboration among clinicians, dermatologists, pathologists, and radiology professionals.

Objectives:

• Identify the typical clinical presentation of mastocytoma and other forms of cutaneous mastocytosis, including age-related differences and common mimickers.
• Differentiate mastocytoma from other benign and inflammatory cutaneous lesions by comparing key histopathologic features.
• Assess patients with suspected mastocytoma to determine when evaluation for systemic mastocytosis is indicated, including appropriate laboratory and referral considerations.
• Collaborate with dermatology, pathology, radiology, and pediatric clinicians to support accurate diagnosis, risk assessment, and coordinated follow-up.

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Introduction

A mastocytoma is a tumor of mast cells, which derive from myeloid stem cells and are located in connective tissues, predominantly in the skin and mucosal linings. Mast cell cytoplasmic granules are filled with histamine, peptides, and other mediators that play an active role in immune responses, especially in allergic and anaphylactic reactions.[1] Clonal proliferation of neoplastic mast cells can lead to localized and systemic manifestations,[2] collectively termed mastocytosis and classified as a myeloproliferative disorder by the World Health Organization classification of tumors of hematopoietic and lymphoid tissues. Most patients with mastocytosis have skin involvement; whereas cutaneous disease is localized to the skin, systemic mastocytosis involves one or more extracutaneous organs. In adults, the disease tends to be chronic and systemic, whereas purely cutaneous mastocytosis is usually seen in childhood (see Image. Mastocytoma). Cutaneous mastocytosis can range from solitary mastocytoma to diffuse erythrodermic mastocytosis, most commonly presenting as maculopapular lesions known as urticaria pigmentosa.[3][4] Please see StatPearls' companion reference, "Urticaria Pigmentosa," for further information.

Etiology

Although the etiology of the disease is not fully elucidated, the microenvironment of lesional tissue shows elevated concentrations of growth factors and interleukins that induce mast cell and melanocyte proliferation and inhibit mast cell apoptosis, which may play a role.[5][6][7] Somatic mutations in the KIT gene, particularly gain-of-function mutations found in more than 90% of adults with the disease, lead to increased activation of mast cell growth factor and are implicated, though they may not be the initiating factor in the proliferation of abnormal mast cells.[8] The most common KIT gene mutation is D816V at codon 816, an aspartic acid-to-valine substitution, found in both adult and childhood cases, and it leads to activation of the KIT receptor. Although these mutations are somatic, rare familial cases have also been reported in an autosomal dominant fashion.[9] 

Epidemiology

Cutaneous mastocytosis without systemic involvement tends to affect children, with most patients presenting during the first 2 years of life.[10] Both mastocytoma and urticaria pigmentosa lesions can also be present at birth. Urticaria pigmentosa accounts for 70% to 90% of cases, followed by mastocytomas or nodular proliferations in 10% to 35% of cases of cutaneous mastocytosis.[2] Diffuse involvement is rare, comprising only 1% to 3% of cases.[2] Mastocytomas are usually solitary, although multiple lesions are possible, typically fewer than 4. The disease shows no predilection for sex, race, or ethnicity. Rare cases of adult-onset cutaneous mastocytoma have also been reported in the literature.[11]

Pathophysiology

While the accumulation of mast cells appears as maculopapular or nodular lesions, physical stimuli such as rubbing or pressure on the lesion trigger mast cell degranulation, releasing histamine, leukotrienes, and prostaglandins that cause localized and systemic symptoms.[12]

Histopathology

Due to histopathologic heterogeneity, standardized diagnostic criteria are lacking; however, proposed thresholds for mast cell density range from 75 to 250 cells/mm², with counts exceeding 250 cells/mm² generally considered diagnostic.[13] Histologic examination shows a dermal infiltrate of mast cells, primarily in the papillary dermis, that can be accompanied by dermal edema and eosinophils. Mast cells tend to aggregate around blood vessels and appear as spindle- to round-shaped cells with pale granular cytoplasm and pale nuclei (see Image. Solitary Mastocytoma of Skin). Nuclear pleomorphism and lobation have also been reported in rare case reports.[11] However, frank nuclear atypia is not seen and should raise suspicion for malignant transformation. Infrequent mitoses can be observed. Deep dermal and subcutaneous infiltration can be seen in nodular forms. Giemsa or toluidine blue staining highlights metachromatic granules, whereas immunophenotypic expression of tryptase, CD117, and KIT establishes the cell of origin. Aberrant immunophenotypic expression or flow cytometric findings positive for CD25 and, less commonly, CD2 can confirm the neoplastic nature of mast cells; however, these findings are not required for diagnosis.

History and Physical

Cutaneous mastocytosis can involve any part of the body, but the disease is most commonly found on the trunk and extremities. Lesions can be single or few, vary in size, and appear as yellowish-brown pigmented macules, papules, or nodules. The lesions are generally nontender but can be associated with intermittent pruritus and erythema. Rubbing or stroking the lesion can degranulate mast cells and cause flushing, pruritus, and skin swelling, known as the Darier sign, which is pathognomonic for the disease.[14] Blistering and bullous presentations are common in children younger than 3 years and can also be present in diffuse and severe forms of the disease. The difference between mastocytoma and urticaria pigmentosa is based on the number of lesions: when 3 or fewer nodules are present, the lesion is classified as a mastocytoma. Diffuse disease presents with thickened, leathery skin without individual lesions.

Telangiectasia macularis eruptiva perstans is an extremely uncommon variant that may present as red telangiectatic macules and may be found in conjunction with urticaria pigmentosa.[15][16] Scarring does not result from any of the lesions. Although systemic involvement does not occur in cutaneous mastocytosis, symptoms of wheezing and syncope have been reported. Gastrointestinal tract symptoms, including diarrhea, have been reported in about 40% of children. Alternatively, acute mast cell activation with anaphylactic symptoms may also occur.

Evaluation

Although cutaneous mastocytoma or mastocytosis may be suspected based on the physical appearance of the lesions, particularly if the Darier sign is present, histology and molecular tests may be required, especially in subtle cases.[3] The WHO classification requires both clinical and histologic findings and the exclusion of systemic disease before making a diagnosis of cutaneous mastocytosis or mastocytoma. Fine-needle aspiration of the lesion is sufficient to diagnose mast cell proliferation. However, a surgical biopsy may be required to fully differentiate the cells, as they can range from well- to poorly differentiated. The disease is classified into 4 stages based on WHO criteria.

Dermatoscopy findings are nonspecific. Baseline serum tryptase levels should be measured, and a complete blood cell count should be obtained before therapy. Elevated serum tryptase levels and bone marrow involvement are generally not seen in pediatric cutaneous disease but may be present in adults. Pediatric cases with systemic symptoms, an abnormal complete blood cell count, insufficient response to symptomatic therapy, and elevated tryptase levels can also be evaluated for bone marrow abnormalities. Abdominal ultrasonography can be performed to exclude organomegaly.

Treatment / Management

Treatment is symptomatic and aims to reduce triggers (eg, rubbing, temperature changes, dryness) that may cause mast cell mediator release. Oral antihistamines are typically first-line therapy, and topical corticosteroids (usually a potent corticosteroid) are generally used to alleviate symptoms. In addition to topical corticosteroids or topical tacrolimus, intralesional corticosteroids can also be injected into the lesion. Phototherapy has also been used to relieve pruritus. Cytoreductive and surgical therapy are reserved for systemic cases. Surgical resection is also used for solitary large tumors or for cosmetic purposes. Epinephrine should be used in any case of suspected anaphylaxis. Treatment, especially in children with solitary cutaneous mastocytoma, requires close observation because, given their benign nature, most of these lesions tend to resolve spontaneously before puberty.

Differential Diagnosis

Several conditions can mimic mastocytoma or mastocytosis and should be considered in the differential diagnosis. Differential diagnoses include the following:

• Carcinoid syndrome: Flushing and diarrhea overlap with mast cell mediator symptoms.
• Pheochromocytoma: Episodic flushing, hypertension, and tachycardia can mimic mast cell activation.
• Hereditary or acquired angioedema: Recurrent swelling may suggest mastocytosis.
• Gastrinoma and parathyroid tumors: Gastrointestinal tract symptoms and elevated tryptase levels may overlap with mastocytosis.
• Myeloproliferative neoplasms with eosinophilia (eg, FIP1L1::PDGFRA) can feature spindle-shaped CD25-positive mast cells that mimic mastocytoma.
• Inflammatory dermatoses: Inflammatory dermatoses (eg, psoriasis, atopic dermatitis, lichen planus, prurigo) may feature reactive mast cell hyperplasia on biopsy, mimicking cutaneous mastocytosis histologically.
• Metastatic disease and metabolic bone conditions: Metastatic disease and metabolic bone conditions can mimic skeletal findings of systemic mastocytosis on imaging.
• Mast cell activation syndrome: Secondary or idiopathic mast cell activation syndrome presents with mediator-related symptoms in the absence of clonal mast cell proliferation.

Staging

The WHO staging system classifies the disease into 4 stages based on the number of lesions, the involvement of lymph nodes, and distant metastases:

• Stage I: The disease is confined to a single lesion without lymph node involvement.
• Stage II: A solitary skin lesion involves adjacent lymph nodes.
• Stage III: Multiple lesions are present, or a large lesion invades deeply into the skin, with or without lymph node involvement.
• Stage IV: The mast cell tumor has metastasized, usually to the spleen, liver, or bone marrow.

Prognosis

Cutaneous mastocytosis follows a benign course and overall carries a good long-term prognosis. Children with disease onset before age 2 generally achieve complete resolution by age 10.[17] Unresolved cases and cases in patients older than 2 years are likely to persist. Although adult-onset cases usually manifest with systemic symptoms, persistent cases from childhood can occasionally progress to systemic disease. Pediatric cases associated with an increased risk of systemic disease include those with disease onset after age 2 years, symptoms that persist beyond adolescence, or abnormal blood count results. Both persistent and adult-onset disease, albeit rare, carry a risk of malignant sarcomatous transformation (characterized by atypical mast cells) or leukemic transformation (characterized by atypical, immature mast cells in the blood).[18][19]

Complications

Complications of mastocytosis include the following:

• Persistent disease
• Systemic involvement, including anaphylaxis
• Malignant transformation to mast cell sarcoma or mast cell leukemia, although rare

Deterrence and Patient Education

Patient should be educated on the following:

• Identifying and avoiding stimuli that trigger symptoms
• Patients with systemic disease should be aware of the possibility of anaphylaxis and must carry injectable epinephrine

Pearls and Other Issues

Darier sign may be present in only half of the cases. 

Enhancing Healthcare Team Outcomes

Although pediatricians may be the first clinicians to encounter the disease, a dermatology consultation remains essential. Histologic confirmation is one of the diagnostic criteria; thus, a pathologist's interpretation is also required for a definitive diagnosis. Radiology can be involved in cases with systemic involvement to localize subclinical organomegaly, if present. Clinicians should educate the patient about avoiding triggers. All patients should be educated on how to use epinephrine and carry it with them at all times. A bracelet containing identification and medical information is highly recommended for patients with a history of anaphylactic reaction. Patients with cutaneous mastocytosis have a good prognosis, but those with a malignant cause have a guarded prognosis.[20]

Review Questions

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References

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Swarnkar B, Sarkar R. Childhood Cutaneous Mastocytosis: Revisited. Indian J Dermatol. 2023 Jan-Feb;68(1):121. [PMC free article: PMC10162768] [PubMed: 37151240]

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Brockow K, Akin C, Huber M, Scott LM, Schwartz LB, Metcalfe DD. Levels of mast-cell growth factors in plasma and in suction skin blister fluid in adults with mastocytosis: correlation with dermal mast-cell numbers and mast-cell tryptase. J Allergy Clin Immunol. 2002 Jan;109(1):82-8. [PubMed: 11799370]

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Reed JA, McNutt NS, Bogdany JK, Albino AP. Expression of the mast cell growth factor interleukin-3 in melanocytic lesions correlates with an increased number of mast cells in the perilesional stroma: implications for melanoma progression. J Cutan Pathol. 1996 Dec;23(6):495-505. [PubMed: 9001979]

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Longley BJ, Tyrrell L, Lu SZ, Ma YS, Langley K, Ding TG, Duffy T, Jacobs P, Tang LH, Modlin I. Somatic c-KIT activating mutation in urticaria pigmentosa and aggressive mastocytosis: establishment of clonality in a human mast cell neoplasm. Nat Genet. 1996 Mar;12(3):312-4. [PubMed: 8589724]

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Fett NM, Teng J, Longley BJ. Familial urticaria pigmentosa: report of a family and review of the role of KIT mutations. Am J Dermatopathol. 2013 Feb;35(1):113-6. [PubMed: 22892471]

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Kettelhut BV, Metcalfe DD. Pediatric mastocytosis. Ann Allergy. 1994 Sep;73(3):197-202; quiz 202-7. [PubMed: 8092552]

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Exposito-Serrano V, Agut-Busquet E, Leal Canosa L, Herrerías Moreno J, Saez A, Luelmo J. Pleomorphic mastocytoma in an adult. J Cutan Pathol. 2018 Feb;45(2):176-179. [PubMed: 29148588]

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Stafford HD, Hunt RD. Darier's Sign in Solitary Mastocytoma. N Engl J Med. 2025 Jan 30;392(5):494. [PubMed: 39879595]

13.

Damman J, Diercks GFH, van Doorn MB, Pasmans SG, Hermans MAW. Cutaneous Lesions of Mastocytosis: Mast Cell Count, Morphology, and Immunomolecular Phenotype. Am J Dermatopathol. 2023 Oct 01;45(10):697-703. [PubMed: 37378479]

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Bennani K, Gallouj S, El Bakkali M, El Jouari O. Infantile Mastocytoma: Clinical Presentation and Diagnostic Insights. Cureus. 2026 May;18(5):e108107. [PMC free article: PMC13222670] [PubMed: 42226882]

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Kikina S, Ali L, Audet S, Koleva E, Imran A, Morley G, Alhameedi HN. Widespread Progressive Telangiectasia in a 54-Year-Old Caucasian Male. Cureus. 2025 Oct;17(10):e94588. [PMC free article: PMC12614912] [PubMed: 41246743]

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Auquit-Auckbur I, Lazar C, Deneuve S, Guillemet C, Cordel N, Blanchard F, Joly P, Courville P. Malignant transformation of mastocytoma developed on skin mastocytosis into cutaneous mast cell sarcoma. Am J Surg Pathol. 2012 May;36(5):779-82. [PubMed: 22498828]

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Disclosure: Aadil Ahmed declares no relevant financial relationships with ineligible companies.

Disclosure: Nishad Sathe declares no relevant financial relationships with ineligible companies.

Disclosure: Arif Jan declares no relevant financial relationships with ineligible companies.