In tumour cytology, cells are evaluated for the presence of morphological alterations compared with the normal cells from which they originate. When present, these changes are referred to as criteria of malignancy.
In malignant tumours, with the exception of well-differentiated forms and some specific neoplasms, most neoplastic cells show multiple morphological features of atypia. However, some of these changes can also be induced by severe inflammation. For this reason, caution should be exercised in diagnosing neoplasia in the presence of numerous inflammatory cells. In all those cases where a definitive diagnosis is not possible, histopathological examination should be recommended.
The main cytological criteria used to identify malignancy are described in the following sections. Nuclear criteria are considered more significant because they are less likely to be induced by non-neoplastic processes such as inflammation.
4.1 General Criteria of Malignancy
• Arrangement
Arrangement is mostly evaluated in epithelial tumours. In non-neoplastic epithelial lesions and in benign epithelial tumours, cells are generally uniformly arranged and mirror the architecture of the normal tissue from which they arise. In malignant tumours, cells undergo an uncontrolled and haphazard growth that can lead to disorganized architectures. Cytologically, this can be observed as nuclear moulding (nucleus of one cell to deform around the nucleus of another cell) and cell crowding (overlapping of nuclei).
• Anisocytosis and macrocytosis
Anisocytosis (cell size variation) and macrocytosis (presence of exceptionally large cells) should be interpreted in the context of the tissue examined. A mild degree of size variation is considered normal. Moderate to marked anisocytosis is usually considered significant, although this should be interpreted in the context of the characteristics of the tissue of origin.
• Pleomorphism
Pleomorphism is variability in shapes within the same cell type.
• Loss of cohesion
Loss of cohesion is the result of down-regulation of the adhesion cellular molecules. This phenomenon is typically observed in epithelial tumours and is usually associated with increased exfoliation upon aspiration.
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