What is a large cell acanthoma?

What is a Large Cell Acanthoma?

Large cell acanthoma (LCA) is a benign epidermal neoplasm characterized by a sharply demarcated proliferation of uniformly enlarged keratinocytes (both nucleus and cytoplasm approximately twice the size of adjacent normal cells), typically presenting as a pigmented or skin-colored macule or papule in sun-exposed areas of middle-aged to elderly patients, predominantly women. 1

Clinical Characteristics

LCA presents with the following features:

• Patient demographics: Primarily affects adults with mean age around 70 years, with a strong female predominance (female:male ratio of 4:1) 1
• Appearance: Most commonly presents as a pigmented macule or papule, though can be skin-colored or even hypopigmented (distinguishing it from solar lentigo) 2
• Surface texture: May have a verrucous or slightly keratotic surface 3
• Size: Usually less than 10mm in diameter 3
• Location: Predominantly found on sun-exposed areas including the face, upper limbs, and lower extremities 1
• Duration: Mean disease duration of approximately 1.6 years before diagnosis 1

Dermoscopic Features

Dermoscopy significantly aids in distinguishing LCA from other epidermal tumors 4:

• Yellow opaque homogeneous background (common finding)
• Brown dots (common finding)
• Moth-eaten border (common finding)
• Prominent skin markings (distinguishing feature)
• Short white streaks (distinguishing feature)

Histopathological Features

The defining microscopic characteristics include 1:

• Sharply demarcated epidermal lesion with clear lateral borders
• Uniformly enlarged keratinocytes (approximately twice the size of adjacent normal cells)
• Hypergranulosis beneath hyperorthokeratosis
• Accentuated stratum lucidum (present in 80% of cases)
• Occasional accentuation of papillary outline
• In pigmented forms, immunohistochemistry shows no increase in melanocyte count

Nosologic Controversy

There is ongoing debate about whether LCA represents a distinct entity:

• Some authors consider it a variant of solar lentigo with cellular hypertrophy, noting similar morphologic attributes but different immunophenotypes (keratin 10 and Bcl-2 expression) 5
• Others argue it is a distinct entity based on: the existence of hypopigmented forms (unlike solar lentigo), absence of elongated hyperpigmented keratinocyte buds characteristic of solar lentigo, and hyperploid (rather than diploid) keratinocytes 1, 2
• Historical perspective: Some have suggested it represents a cytologic variant of Bowen's disease based on disordered malpighian cells, nuclear variability, occasional dyskeratoses, and suprabasal mitoses 3

Clinical Significance

LCA is a benign lesion with no malignant potential. However, it is frequently underdiagnosed because:

• Clinicians often fail to recognize it (not clinically suspected in 60% of cases even by dermatologists) 1
• It occurs in only 1-2.55 per 1,000 cutaneous biopsies, making it relatively uncommon 3
• It shares overlapping features with other pigmented epidermal tumors

Important Caveats

• Do not confuse LCA with clear cell acanthoma (CCA), which is an entirely different entity characterized by keratinocytes with clear cytoplasm, typically presenting on lower extremities with a peripheral scaling collarette and "string of pearls" vessels on dermoscopy 6
• Multiple LCA lesions can occur but are rare, typically affecting limbs and back 3
• The lesion requires histopathological confirmation for definitive diagnosis, as clinical diagnosis alone is unreliable