Cytological versus histopathological diagnosis in canine osteosarcoma.

The role of cytology in the diagnosis of primary bone tumours is less established
and perhaps not comprehensively studied compared with the diagnosis of
soft tissue tumours. We evaluated the diagnostic accuracy of the cytological
examination of canine osteosarcoma, comparing the cytological diagnoses
offered with subsequent histopathological diagnoses on the same lesions.
One hundred and eighty-four histologically confirmed canine osteosarcoma
cases were retrieved from the University of Queensland veterinary pathology archives, 27 (15 per cent) of which were examined cytologically. In three cases (11 per cent) the cytological diagnosis was not specific or the examination was inconclusive. In five (19 per cent) the cytological diagnosis did not agree with the histopathological diagnosis and was considered misleading. The cytological diagnosis was osteosarcoma, in full agreement with the histopathological diagnosis, in six of the 27 cases (22 per cent); sarcoma (that is, it
differentiated between sarcomatous and carcinomatous malignancies), in a further eight cases (30 per cent); and a malignancy in five (19 per cent). Nineteen cases (70 per cent) had cytological and histopathological diagnoses in partial or full agreement. Cytology was misleading to a degree comparable with that of histopathological diagnosis observed in the same series (18 per cent and 20 per cent respectively, P. Loukopoulos, unpublished data). Sensitivity of 65 per cent and accuracy of 95 per cent has been reported for the cytological diagnosis of human osteosarcoma. Comparisons of cytological with subsequent
histopathological diagnosis are very sparse in the veterinary literature,
despite the common use of the technique in practice. A study of 140 cases reported a partial or full agreement between cytology and histopathology of 90 per cent, which is higher than the one reported here. In a more recent study of 269 samples from various species, the sensitivity of cytological examination ranged from 33·3 to 66·1 per cent and depended on the location of the
lesion, being most accurate for cutaneous and subcutaneous lesions and least accurate for liver lesions, and on the type of lesion. It was most effective in the diagnosis of neoplasia and least effective in the diagnosis of dysplasia or hyperplasia. Good correspondence was shown between cytological and histopathological diagnoses of external ear masses in the cat,
with 100 per cent (27 of 27) agreement in the diagnosis of inflammatory polyps v neoplasia; histopathological examination was, however, recommended for differentiation of benign proliferation and malignant
neoplasia. Although only 22 per cent of cases in our series provided a preliminary cytological diagnosis that was in full agreement
with the conclusive histopathological diagnosis of osteosarcoma, in 70
per cent of cases cytological examination was accurate enough to differentiate
between a malignant and a non-malignant lesion, which is often sufficient for
the clinician to proceed to the next step of dealing with the case, particularly when combined with clinical and imaging data. A larger number of cases needs to be examined to confirm these results.
However, based on the above, the cytological evaluation of canine osteosarcoma
patients is adequately accurate and useful to be justified, provided it is followed by histopathological confirmation.