tonsillar SQUAMOUS CELL CARCINOMA IN DOGS
Background
Tonsillar squamous cell carcinoma is a more aggressive tumor than either gingival or lingual squamous cell carcinoma. The median age of dogs with this disease is 9 to 11 years.There appears to be a male predisposition.
No breed predisposition has been described. Occasionally, tonsillar squamous cell carcinoma may occur bilaterally.Clinical Parameters
Dogs with tonsillar squamous cell carcinoma usually present with dysphagia, anorexia, and pain. Owners may have noticed a cervical swelling, which is usually lymph node metastasis rather than primary tumor. Most dogs have shown these signs for 1 month or less, although some dogs may show signs for up to 3 months before presentation.
Clinical Work-up
All dogs with oral tumors should have a thorough examination of both tonsils and aspiration cytologic examination of the local lymph nodes, which may confirm metastatic carcinoma, in addition to a complete blood count, biochemical profile, urinalysis, and skull, thoracic, and abdominal radiographs or ultrasound. Occasionally dogs with this disease may be seen for a cervical swelling, and upon oral examination a tonsillar swelling is noted. If no diagnosis can be reached, biopsy of the tonsil and the regional lymph node is warranted. Thoracic radiographs should be taken, although metastasis is unlikely to be seen at the time of diagnosis. If treatment is undertaken, radiographs should be repeated at regular intervals to screen for metastasis. In view of the high reported rate of intraabdominal metastases in one study, abdominal radiographs and ultrasonography should be performed before any definitive treatment. Abdominal imaging may also be useful for monitoring the patient for metastases after treatment.
Tonsillar squamous cell carcinoma commonly metastasizes to the local lymph nodes. In one study all 22 dogs had lymphadenopathy, as well as infiltrative primary tumors, at the time of diagnosis.
Despite early spread to the lymph nodes, pulmonary metastases are rarely noted at diagnosis. After treatment 9 (33%) of 27 dogs had evidence of distant metastases. In two earlier studies 77 (85%) of 91 dogs with tonsillar squamous cell carcinoma had metastasis to regional lymph nodes at necropsy. Systemic metastases were less common; they occurred in the lung, spleen, liver, and thyroid gland. In a smaller group of dogs, metastasis to the spleen and liver occurred more often than to the lungs.Therapeutic Approach
Surgery alone is rarely effective in the treatment of tonsillar squamous cell carcinoma due to a high metastatic rate, which manifests early in the course of the disease.A combination of surgery and radiation provided good local control at radiation doses of 35 Gy to 42.5 Gy; six of eight dogs showed a complete response, and one dog showed a partial response. Recurrence was seen in only two of the seven responding dogs, although metastatic disease to the spleen, liver, bone, and lungs was seen or suspected in all seven. Survival ranged from 44 to 631 days, with a median of 109 days.
In another study, dogs were treated with a combination of surgery, orthovoltage radiation therapy, and chemotherapy that alternated doxorubicin (30 mg/m2 intravenously every 3 weeks) with cisplatin (60 mg/m2 intravenously every 3 weeks). Of 6 dogs receiving this protocol, 5 achieved a complete response,with a median survival of 240 days. Four of these dogs developed tumor recurrence and metastatic disease. In comparison, 16 dogs had no response to treatment with this chemotherapy protocol (or combinations of doxorubicin, vinblastine, cisplatin, and cyclophosphamide) when it was administered without radiation therapy. Median survival for these 16 dogs was 105 days. Piroxicam may be a good option for analgesia and also because it has anticancer effects.
Aggressive surgery and radiation therapy, combined with doxorubicin and cisplatin chemotherapy, provide the best therapeutic results for this tumor; even then, tumor progression is difficult to control. The prognosis for dogs with tonsillar squamous cell carcinoma is poor.