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Does cell-free DNA diagnose iris melanoma in cats?

Rushton JG, Ertl R, et al. Circulating cell-free DNA does not harbor a diagnostic benefit in cats with feline diffuse iris melanomas. J Feline Med Surg. 2018 Mar 1:1098612X18762017. doi: 10.1177/1098612X18762017. (Winn-funded study)

The most common intraocular tumor in cats is feline diffuse iris melanoma (FDIM). This tumor will present as a nodular or diffuse accumulation of pigment within the iris. FDIMs are potentially highly malignant with a metastasis rate between 19% and 63% to liver, lung, spleen, lymph nodes and/or bone. The mean age of cats with FDIM is eleven years, so the condition is diagnosed primarily in middle-aged to older cats.

The gold standard for diagnosis is histopathological examination of affected tissue, otherwise the only tentative diagnostic tool available for veterinarians and veterinary ophthalmologists is an ophthalmological examination. As clinicians, they are faced with a diagnostic dilemma of monitoring the affected eye, with the possibility of metastasis occurring, or enucleating a frequently visual eye.

In people and in dogs, cell-free DNA (cfDNA) or liquid biopsy has been shown to be of use as diagnostic and prognostic markers in cancer patients. This diagnostic process has never been studied in cats with ocular melanomas. The investigators’ aim in this study was to evaluate cfDNA concentration levels and fragmentation (integrity) in the blood of cats with FDIMs and cats with iris naevi (benign pigmentation changes), as well as cats without ocular abnormalities, so to evaluate the use of cfDNA as a diagnostic and/or prognostic marker for cats with FDIMs.

This study included 33 cats with melanoma, 30 cats with iris naevi and 31 control cats. The overall median age of the patients was 7 years. The different cat breeds included were domestic shorthair (n=73), British Shorthair (n=7), Maine Coon (n=7), domestic longhair (n=2), Chartreux (n=2), Persian (n=2) and other breeds (n=1). The cfDNA concentrations did not significantly differ between breeds.

The authors found after quantitative PCRs of extracted cfDNA from plasma samples that the cfDNA concentration and integrity analysis resulted in no significant differences between cats with iris melanoma, iris naevus or the control group. In cats with suspected or proven metastases did not show higher cfDNA levels than those cats without metastases. The conclusion was cfDNA is not adequate as a marker for iris melanomas in cats. (VT)

See also:

Wiggans KT, Reilly CM, et al. Histologic and immunohistochemical predictors of clinical behavior for feline diffuse iris melanoma. Vet Ophthalmol. 2016 Jul;19 Suppl 1:44-55.