nonsquamous

Nonsquamous, or non-squamous, is a histopathological descriptor used to indicate that a tissue or tumor does not show squamous differentiation. It is commonly used in pathology reports to distinguish neoplasms that originate from squamous epithelium from those that arise from other histologic lineages. The term is not a diagnosis by itself but a classification that helps guide reporting and treatment decisions.

In the context of lung cancer, non-squamous non-small cell lung cancer (NSCLC) includes histologies such as adenocarcinoma and large cell carcinoma. This distinction is clinically relevant because certain therapies and safety considerations differ by histology. For example, some anti-angiogenic treatments are recommended only for non-squamous NSCLC due to associated risks in squamous tumors. Pathologists determine nonsquamous status based on morphological features and, when necessary, immunohistochemical staining. Typical markers used include p40 or p63 to indicate squamous differentiation (often negative in nonsquamous tumors) and markers like TTF-1 and Napsin A that support adenocarcinoma.

Limitations exist: tumors can exhibit mixed or focal squamous differentiation, known as adenosquamous carcinoma, which may be reported as having both components. In such cases, the descriptive emphasis may shift toward identifying the predominant histology and any mixed features. The term nonsquamous therefore serves as a practical histologic category rather than a stand-alone diagnosis.

See also: squamous cell carcinoma, non-small cell lung cancer, histopathology.