Cytology — Examination of Single Cells

Cytology evaluates cellular morphology, nuclear characteristics, and architectural arrangements to identify premalignant or malignant alterations. Cells are harvested through exfoliation (such as cervical Pap smears or urine samples) or through fine-needle aspiration (FNA) of suspicious lumps and internal organs. The harvested specimens are smeared onto glass slides, stained, and examined by a cytopathologist.

Pathologists assess criteria such as nuclear enlargement, irregular nuclear membranes, chromatin clumping, and altered nucleus-to-cytoplasm ratios. While cytology offers rapid, minimally invasive diagnostic insights, it provides less structural context than a surgical core biopsy, sometimes necessitating reflex histology or immunocytochemistry to establish a definitive diagnosis.

Cytology provides an initial, low-risk route to cancer screening and diagnosis. Because it relies on gentle sampling methods, patients experience fewer complications and quicker recoveries compared to surgical procedures. A timely cytology report can rapidly confirm cancer recurrence, identify the cause of fluid build-up, or confirm that an enlarged thyroid nodule is benign, preventing unnecessary surgeries.

Cytological analysis uses specialised stains, such as Papanicolaou or Giemsa stains, to highlight cellular features under light microscopy. To enhance diagnostic precision, laboratories often create cell blocks from liquid samples, allowing immunocytochemistry (ICC) to test for diagnostic protein markers (such as TTF-1, p63, or calretinin) and molecular assays like EGFR mutation testing on aspirated cellular material.

Cytology is routinely used in screening for cervical cancer via cervical smear testing. It is also central to evaluating thyroid nodules, breast lumps, salivary gland tumours, and enlarged lymph nodes via fine-needle aspiration. Additionally, cytology assesses pleural and peritoneal fluids to check for metastatic involvement from lung, ovarian, pancreatic, and gastrointestinal cancers.

A cytological diagnosis can confirm disease recurrence or metastasis without the need for major operations, enabling oncologists to initiate chemotherapy, immunotherapy, or targeted therapies promptly. For thyroid nodules, cytology results categorised by systems like Bethesda guide whether a patient needs active surveillance, partial thyroidectomy, or total thyroidectomy.