Using radiation therapy as the primary treatment for oral squamous cell carcinoma has theoretical advantages compared with
other treatment methods,5 including the ability to treat large inoperable tumors and to treat tumors without patient disfigurement. Additionally,
regional lymph nodes can be included in the radiation field. A notable disadvantage with radiation as the sole therapy is
that bulky tumors tend to exhibit radiation resistance. Additionally, mucositis, which usually develops in the final stages
of radiation treatment and generally lasts for one to three weeks after the completion of treatment, can make supportive therapy
such as a feeding tube a necessity. Definitive radiation therapy (small, frequent doses) has been reported in a number of
settings and is discussed below in those respective areas. The use of palliative radiation and accelerated radiation therapy
has been evaluated individually as follows.19,20
One study looked at seven cats with advanced, inoperable oral squamous cell carcinoma.19 The cats were treated with palliative radiotherapy and variable adjuvant chemotherapy with mitoxantrone, piroxicam, or acupuncture.
Megavoltage radiation in 8-gray (Gy) fractions was delivered on Days 0, 7, and 21 for a total dose of 24 Gy. While the small
sample size makes it difficult to draw definitive conclusions regarding the efficacy of palliative radiation, the fact that
six of the seven cats were euthanized because of tumor growth or radiation side effects with a median survival time of only
60 days does not support radiation therapy's use in these patients.19
A pilot study involving an accelerated radiation therapy protocol in eight cats with squamous cell carcinoma was recently
reported.20 Over nine days, these cats received seven days of treatment with twice-daily 3.5-Gy fractions for a total dose of 49 Gy.
The tumors treated included three lingual tumors, one tonsillar tumor, two mandibular tumors, one cheek tumor, and two large
cutaneous lesions; the two cutaneous lesions were in one cat. Treatment fields included the tumor, 1-cm margins, and tumor-draining
lymph nodes. Five of the cats were judged to have complete responses, but the survival median for all cats was only 86 days.
Overall, the accelerated treatment was well-tolerated by all cats. Despite the poor overall survival time, further studies
may be warranted because of the apparent high response rate.20
Chemotherapy and chemotherapy with radiation
Chemotherapy alone has shown minimal effect against oral squamous cell carcinoma in cats. In some studies, chemotherapy has
been more successful when combined with radiation therapy.
Doxorubicin and cyclophosphamide. A protocol using doxorubicin and cyclophosphamide had poor efficacy, with only one of five cats with oral squamous cell carcinoma
showing a response (partial) to treatment.21 The median survival time of the five cats was 30 days.21
Cisplatin. To date cisplatin, or cis-diamminedichloroplatinum (II), is the most effective chemotherapeutic agent in treating human head and neck squamous cell
carcinoma.22 While cisplatin leads to pulmonary vasculitis and death in cats, a second-generation cisplatin analogue, cis-bis-neodecanoato-trans-R,R-1,2-diaminocyclohexane
platinum (II) (NDDP), can be liposome-encapsulated (L-NDDP) and safely administered.22 In one study, 18 cats with advanced squamous cell carcinoma disease (World Health Organization's clinical stage II, III,
or IV) were treated with L-NDDP at doses ranging from 75 to 100 mg/m2 every 21 days.22 Unfortunately, no clinical responses were seen.
Mitoxantrone and radiation therapy. Mitoxantrone is a dihydroxyquinone derivative of anthracene related to doxorubicin.23 In a study evaluating the toxicity and efficacy of mitoxantrone in cats with malignant tumors, 32 cats with oral squamous
cell carcinoma were treated with single-agent mitoxantrone.23 Because of their poor response, 11 cats with squamous cell carcinoma were then treated concurrently with radiation (44-
to 65-Gy, 10 to 15 fractions over a three-week period) beginning with the first dose of mitoxantrone (2.5 to 6 mg/m2 ). Four of the cats had sublingual squamous cell carcinoma; the other seven cats had a tumor of the mandible or maxilla.
Further information on the stage of the tumors was not provided. None of the cats had signs of toxicosis attributable to the
chemotherapy; mucositis consistent with radiation therapy was noted but not described in detail. Eight of the 11 cats went
into complete remission (median remission duration of 170 days; range 28 to 485 days), and one cat had a partial remission
that lasted 60 days.23 Survival times were not discussed.
While the response rate for combined mitoxantrone and radiation therapy is encouraging, the duration of response is short.
As squamous cell carcinoma involving the mandible or maxilla is highly infiltrative into bone, accurate determination of a
complete remission is difficult without detailed imaging such as computed tomography. How remission status was determined
was not discussed. If only visible gross disease was assessed, the complete remission rate may have been overestimated, contributing
to the short duration of remission.