JAVMA • Vol 252 • No. 11 • June 1, 2018 1393 Small Animals & Exotic M ore than 80% of all mammary gland masses in cats are malignant, and the behavior of these tumors is characterized by local invasion into the vasculature and surrounding tissues and metastasis Association of surgical approach with complication rate, progression-free survival time, and disease-specific survival time in cats with mammary adenocarcinoma: 107 cases (1991–2014) Francesco Gemignani DVM Philipp D. Mayhew BVM&S Michelle A. Giuffrida VMD Jason Palaigos Jeffrey J. Runge VMD David E. Holt BVSC Nicholas A. Robertson Bernard Seguin DVM Meaghan Walker Ameet Singh DVM Julius M. Liptak BVSC, MVetClinStud Giorgio Romanelli DVM Marina Martano DVM Sarah E. Boston DVM Cassie Lux DVM Roberto Busetto DVM William T. N. Culp VMD Katherine A. Skorupski DVM Jenna H. Burton DVM From the Department of Animal Medicine, Production and Health, University of Padova, 35122 Padova PD, Italy (Gemignani, Busetto); the Department of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California-Davis, Davis, CA 95616 (Mayhew, Giuffrida, Culp, Skorupski, Burton); the Matthew J. Ryan Veterinary Hospital (Palaigos, Runge) and Department of Clinical Studies (Holt), School of Veterinary Medicine, University of Pennsylvania, Philadelphia, PA 19103; the Flint Animal Cancer Center, Colorado State University, Fort Collins, CO 80523 (Robertson, Seguin); the Depart- ment for Clinical Studies, Ontario Veterinary College, University of Guelph, Guelph, ON N1G 2W1, Canada (Walker, Singh); Alta Vista Animal Hospital, 2616 Bank St, Gloucester, ON K1T 1M9, Canada (Liptak); Clinica Veteri- nario Nerviano, Via Giulio Cesare Lampugnani, 3, 20014 Nerviano MI, Italy (Romanelli); the Department of Ani- mal Pathology, School of Veterinary Medicine, University of Turin, 10124 Torino TO, Italy (Martano); the Depart- ment of Small Animal Clinical Studies, College of Veteri- nary Medicine, University of Florida, Gainesville, FL, 32610 (Boston); and the Department of Small Animal Clinical Sciences, College of Veterinary Medicine, University of Tennessee, Knoxville, TN 37996 (Lux). Address correspondence to Dr. Mayhew (philmayhew@ gmail.com). OBJECTIVE To evaluate potential associations between surgical approach and complica- tion rate, progression-free survival time, and disease-specifc survival time in cats with mammary adenocarcinoma. DESIGN Retrospective case series. ANIMALS 107 client-owned cats. PROCEDURES Medical records of cats that underwent surgical excision of mammary ad- enocarcinoma by means of a unilateral or bilateral (staged or single-session) mastectomy at 9 hospitals between 1991 and 2014 were reviewed. Relevant clinicopathologic data and details of surgical and adjuvant treatments were recorded. Outcome data were obtained, including postoperative complica- tions, progression-free survival time, and disease-specifc survival time. RESULTS Complications occurred in 12 of 61 (19.7%) cats treated with unilateral mas- tectomy, 5 of 14 (35.7%) cats treated with staged bilateral mastectomy, and 13 of 32 (40.6%) cats treated with single-session bilateral mastectomy. Complications were signifcantly more likely to occur in cats undergoing bi- lateral versus unilateral mastectomy. Median progression-free survival time was longer for cats treated with bilateral mastectomy (542 days) than for cats treated with unilateral mastectomy (289 days). Signifcant risk factors for disease progression included unilateral mastectomy, tumor ulceration, lymph node metastasis, and tumors arising in the fourth mammary gland. Signifcant risk factors for disease-specifc death included lymph node me- tastasis and development of regional or distant metastasis. Among cats that did not develop metastasis, unilateral mastectomy was a signifcant risk fac- tor for disease-specifc death. Treatment with chemotherapy was associ- ated with a signifcantly decreased risk of disease-specifc death. CONCLUSIONS AND CLINICAL RELEVANCE Results supported bilateral mastectomy for the treatment of mammary ad- enocarcinoma in cats to improve progression-free and disease-specifc sur- vival time. Performing bilateral mastectomy in a staged fashion may help to decrease the complication rate. ( J Am Vet Med Assoc 2018;252:1393–1402) to draining lymph nodes and distant locations, in- cluding the lungs, pleura, and liver. 1–10 Because of this aggressive biological behavior, mammary ad- enocarcinoma requires aggressive treatment in cats. Treatment options that have been reported include surgical excision, chemotherapy, immunotherapy, radiation therapy, and various combinations of these treatments. 1–10 Numerous studies have evaluated ABBREVIATIONS CI Confdence interval HR Hazard ratio