Squamoid

Squamoid is an adjective used in histology and pathology to describe cells or tissues that resemble squamous epithelium in their overall appearance, but are not necessarily true squamous cells. The term derives from the Latin squama, meaning scale, and is used to convey similarity in shape and organization rather than definitive lineage.

Morphology and characteristics: Squamoid cells are typically polygonal and may have eosinophilic cytoplasm, but they do not always display classic features of mature squamous differentiation such as intercellular bridges or keratinization. The descriptor is applied when cells resemble squamous epithelium yet lack confirmed squamous maturation or full keratinization, indicating a resemblance rather than a confirmed identity.

Usage in diagnosis: Pathologists use squamoid to describe areas or cells within lesions that mimic squamous epithelium but do not meet strict criteria for squamous differentiation. This term appears in the assessment of neoplasms with mixed or focal differentiation, such as tumors that show both glandular and squamous-like features, as well as in non-neoplastic lesions where epidermal-like cells are present in atypical locations.

Interpretation and limitations: The squamoid designation is descriptive and not diagnostic of a specific lineage. It should be integrated with other histologic findings, immunohistochemical staining, and clinical context to determine the probable differentiation and potential behavior of a lesion. The term highlights morphological similarity to squamous cells while acknowledging uncertainty about definitive classification.

See also: squamous cell, squamous differentiation, keratinization.