Francesco

This can make the diagnosis very difficult, in particular in amelanotic forms, where melanin granules are either absent or present in very low numbers. In those cases, a definitive diagnosis may require further testing and in particular immunocytochemical stains (ICC).

On a publication from 2015 on 38 cases of canine oral neoplasms, the combination of cytology and ICC (cytokeratin, vimentin, and Melan A) showed a very high sensitivity and specificity for the presurgical diagnosis of amelanotic melanoma. Early identification of this tumour is considered crucial from a clinical point of view, as ability to metastasise to local lymph nodes and other organs is significantly higher than other oral tumours. Treatment involves local tumour control through surgery and/or radiation therapy, as well as systemic treatment.

Heterophils are the counterpart of neutrophils and are seen in selected small mammals, birds, amphibs and reptiles. They are characterised by round to rice shaped brick red granules seen in variable numbers within the cytoplasm.

Foa-Kurloff cells are another leukocyte type that is unique to guinea pigs. They are specialized mononuclear cells that contain an intracytoplasmic inclusion body of mucopolysaccharide, which appear variably pink and granular. Although Foa-Kurloff cells can be present in the blood of both males and females, they are most commonly observed in blood smears from pregnant guinea pigs. These cells may be more prominent during pregnancy because they shift from the lungs and spleen to the thymus and placenta under oestrogen stimulation. Foa-Kurloff cells possibly function as natural killer cells.

Spontaneous tumour regression is defined as spontaneous remission or disappearance of a tumour in the absence of any treatment. This can also be observed in animals and in particular in two conditions: cutaneous histiocytoma and transmissible venereal tumour (TVT).

The cytologic algorithm that most closely correlated with histologic grade classified a MCT as high grade if it is (1) poorly granular or (2) has at least 2 of the following 4 features: presence of any mitotic figures, anisokaryosis, binucleation or multinucleation, or nuclear pleomorphism. This system showed a good correlation with clinical behaviour and cytologic high grade tumours were associated with significantly decreased probability of survival. However, both false positive and false negative results occurred, suggesting histopathology grading is still recommended after surgical removal of the mass. Histopathology will also provide important further information, such as surgical margins. In selected cases, from the histology sections it is also possible evaluating proliferative markers (e.g. Ki67) which can provide additional prognostic information.