Feline colonic adenocarcinoma (locally invasive, highly metastatic) requires wide surgical excision (subtotal colectomy), which may be followed by systemic chemotherapy. Carboplatin, a platinum-based alkylating agent, is relatively safe in cats.

This study assessed the safety and efficacy of subtotal colectomy followed by carboplatin chemotherapy. Medical records of 18 cats with colonic adenocarcinoma were reviewed. Clinical presentations included weight loss (n = 14), inappetence (n = 12), vomiting (n = 8), diarrhea (n = 13), and tenesmus (n = 13). Subtotal colectomy was performed in all cats and surgical margins were judged to be complete; however, nodal metastasis was noted in 6 cats. Carboplatin was administered postsurgically at a median dose of 200 mg/m2 (range, 200–245 mg/m2) IV q4wk for a median of 5 doses/cat. There were no treatment delays from myelosuppression or GI toxicity. Adverse effects included mild neutropenia and mild or moderate thrombocytopenia. Cats were restaged 6 months after receiving carboplatin, sooner if signs recurred. Results showed a median disease-free interval of 251 days (range, 37–528 days) and median survival time of 269 days (range, 40–533 days). Weight loss at initial presentation was a positive prognostic predictor of disease-free interval, whereas nodal and distant metastasis were negative prognostic factors of median survival. Carboplatin was concluded to have minimal toxicity and be a reasonable adjunct to surgical treatment.

Commentary
Intestinal carcinomas are the second most common primary GI tumor (behind lymphoma) and the most common colonic tumor. Adenocarcinoma is best treated with subtotal colectomy and adjuvant chemotherapy. GI lymphoma is usually best treated with chemotherapy alone; surgery may be indicated if obstruction or perforation is evident. Ultrasound-guided fine-needle aspiration and cytology can provide a safe, minimally invasive way to distinguish these cancers and should be considered before aggressive therapy.

Median survival in this study evaluating surgery and carboplatin was similar to that in a previous study in which cats were treated with surgery and doxorubicin (251 days versus 280 days).1 Doxorubicin and carboplatin have different mechanisms of action, and cross-resistance is not expected. Therefore, to maximize treatment efficacy, it would be reasonable to consider using both drugs on an alternating basis when treating cats with colonic adenocarcinoma.—Dennis Bailey, DVM, DACVIM (Oncology)

Source
A review of 18 cases of feline colonic adenocarcinoma treated with subtotal colectomies and adjuvant carboplatin. Arteaga TA, McKnight J, Bergman PJ. JAAHA 48:399-404, 2012.

1. Malignant colonic neoplasia in cats: 46 cases (1990-1996). Slawienski MJ, Mauldin GE, Mauldin GN, Patnaik AK. JAVMA 211:878-881, 1997.