A 6-year-old castrated male Labrador Retriever was presented with lymphadenopathy of the right submandibular lymph node. Abdominal ultrasound revealed a hypoechoic splenic mass and sublumbar lymphadenopathy. The right submandibular lymph node lesion was identified as T-cell-rich B-cell lymphoma, characterized by a mixed cell population with large neoplastic B cells(CD20 and CD79a positive)scattered among numerous small non-neoplastic T cells(CD3 positive)and histiocytes(CD18, MHC class Ⅱ and Iba-1 positive). Cytologic evaluation showed tumor cells invading into the spleen and intra-abdominal lymph nodes. The dog received chemotherapy, but it did not respond sufficiently to the treatment and died 54 days after the initial presentation.

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With radiotherapy, local recurrence of nasal tumors remains challenging. Re-irradiation was performed intermittently to control clinical signs until central nervous system(CNS)signs occurred in a 9-year-old spayed Yorkshire terrier that had completed radiotherapy to the nasal cavity 452 days earlier for intranasal adenocarcinoma(44 Gy/11 fractions/1 month). For radiotherapy, a linear accelerator was used with no margin to preserve normal tissues at a radiation dose at the isocenter of 5-8 Gy. Because the tumor responded well, re-irradiation was planned for recurrent clinical signs. On day 1,600, the dog died, allegedly due to tumor progression and CNS invasion or because of brain necrosis as a radiation side effect. Improved survival is considered achievable with re-irradiation.

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Hypofractionated radiotherapy(27-32 Gy/3-4 fractions)was performed in the 3 dogs diagnosed as plasma cell tumors, since complete resection by surgical operation was impossible. In all cases, their tumors were disappeared within 1 to 4 months after radiotherapy. In case1, recurrence has not been noted during a follow-up period of 19 months. Cases 2 and 3 have not showed recurrence for 13 and 6 months, respectively. These results indicated that hypofractionated radiotherapy is effective for canine plasma cell tumors, since reduction of the local mass was seen within a few months.

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