Lesion — Abnormal Tissue Changes Explained

A lesion is fundamentally any localised area of tissue that has sustained architectural damage or abnormal growth compared with surrounding healthy structures. The term is deliberately descriptive and non-specific, used across medical disciplines to characterise everything from a skin ulcer, cyst, or inflammatory patch to an internal mass observed on a radiologic scan. In cancer diagnostics, physicians use 'lesion' as a neutral placeholder before definitive microscopic classification.

Pathologically, lesions are categorised by their underlying aetiology: they may be reactive, resulting from chronic inflammation or physical injury; infectious, caused by microbial processes; benign neoplastic, representing non-cancerous overgrowths; or premalignant and malignant, characterised by uncontrolled cellular division and invasive potential. Establishing a lesion's exact character requires histopathologic examination under a microscope.

Encountering the word 'lesion' on a scan or pathology report can be unsettling, but understanding that it is a neutral descriptor brings valuable perspective. Clear identification of a lesion marks the starting point of an investigative process. Differentiating a benign lesion from an early-stage malignancy allows clinicians to intervene promptly when curative therapy is possible, or avoid unnecessary and potentially invasive treatments when the lesion is benign, preserving organ function and patient peace of mind.

Lesions are initially detected using cross-sectional imaging such as ultrasound, CT, MRI, or PET scans. To determine whether a lesion is malignant, a biopsy is performed using fine needles, core cutters, or surgical excision. Pathologists analyse the sample, performing immunohistochemistry and molecular profiling to detect actionable biomarkers such as EGFR mutations, BRAF alterations, or PD-L1 expression.

Lesions are investigated across virtually all oncology fields. Common examples include suspicious hyperpigmented skin lesions evaluated for melanoma, pulmonary nodules or lesions suspicious for lung carcinoma, focal hepatic lesions that may indicate hepatocellular carcinoma or metastases, osteolytic bone lesions seen in multiple myeloma, and space-occupying intracranial lesions indicating primary or secondary brain tumours.

Treatment depends entirely on tissue pathology. Benign or asymptomatic lesions may require simple watchful waiting or periodic surveillance imaging. Conversely, malignant lesions necessitate targeted oncological therapies. These may include surgical excision with clear margins, stereotactic body radiotherapy (SBRT), local radiofrequency or microwave ablation, or systemic medical therapies, such as chemotherapy, immunotherapy, and targeted kinase inhibitors, designed to shrink widespread lesions.