Mesenchymal tumours (six cases) included three cases of fibrosarcoma (diagnosed in one golden hamster, one Djungarian hamster and one unspecified species); one case of poorly differentiated sarcoma (tumour cells expressed vimentin, clone V9 and α-SMA and were negative for desmin and Iba-1), diagnosed in a Djungarian hamster; one case of simple lipoma, diagnosed in a golden hamster; and one case of epitheliotropic T-cell lymphoma (tumour cells expressed CD3+ and were CD79a and CD20 negative; Figure 4), diagnosed in a golden hamster. Here, ACTA1 is linked to fibrosarcoma.