Histology — Microscopic Study of Tumour Tissue

Histology involves the chemical fixation, embedding, sectioning, and staining of human tissue so that its cellular architecture can be evaluated by light microscopy. In diagnostic oncology, pathologists scrutinise tissue architecture, cell morphology, nuclear characteristics, mitotic rates, and margins. This process determines whether a lesion is benign, pre-invasive, or frankly malignant.

Beyond simply identifying malignancy, histology classifies tumours into specific histological subtypes—such as adenocarcinoma, squamous cell carcinoma, or small cell carcinoma. It also establishes the tumour grade (how closely the tumour cells resemble their normal counterparts), evaluates depth of local invasion, and checks for lymphovascular or perineural invasion, all of which are vital staging parameters.

Histology forms the absolute foundation of modern oncology. Two tumours that look identical on a scan can have completely different cellular origins and respond to entirely different therapies. Your histological diagnosis dictates which treatment protocols are effective, whether surgery is sufficient, or if chemotherapy, radiotherapy, or immunotherapy are required. Without an accurate histological analysis, selecting the right evidence-based treatment plan is impossible.

Histological analysis begins with tissue acquisition through core needle biopsy, excisional biopsy, or surgical resection. The sample is preserved in formalin, embedded in paraffin wax, cut into microscopic ribbons, and stained—traditionally with hematoxylin and eosin (H&E). Pathologists frequently supplement this with immunohistochemistry (IHC) using antibody panels, and they direct suitable tissue areas toward molecular or genomic sequencing tests.

Histology applies to virtually every solid and hematologic tumour. It defines subtypes in lung cancer (differentiating non-small cell from small cell lung cancer), breast cancer (such as invasive ductal versus lobular carcinoma), gastrointestinal tumours (adenocarcinomas versus neuroendocrine tumours), skin cancers (melanoma versus basal or squamous cell carcinoma), and sarcomas.

Because cancer treatment is subtype-specific, histological results directly determine systemic and local therapies. For example, the histology of non-small cell lung cancer determines whether pemetrexed chemotherapy is appropriate, as it works predominantly in adenocarcinomas rather than squamous cell carcinomas. Histological features such as close surgical margins or vascular invasion also dictate whether adjuvant radiotherapy or chemotherapy is necessary after an operation.