disease at surgery, versus 358 days for those with metastatic disease at surgery (Green et al. 2011). Cats with advanced disease (including carcinomatosis) treated with surgery can have long‐term survival (Kosovsky et al. 1988). No proven chemotherapy for ADC, but combination of 5‐fluorouracil and cisplatin may be effective (Stanclift and Gilson 2004), second‐look surgery recommended for evaluation of response to chemotherapy (Stanclift and Gilson 2004). Overall MST in dogs treated with surgical resection was 233 days, sex was a prognostic factor with MST for male dogs 272 days v 28 days for female dogs. In this study, only 2 of 15 dogs received adjuvant chemotherapy (Paoloni et al. 2002). Reported adjuvant chemotherapies in dogs include doxorubicin, carboplatin, gemcitabine, doxorubicin, 9‐aminocamptothecin, cisplatin, and 5‐fluorouracil (Paoloni et al. 2002). Intracavitary chemotherapy for carcinomatosis can extend survival time (ST) (Moore et al. 1991a; Charney et al. 2005). Large intestinal: debilitation and hypoproteinemia may complicate treatment, surgical resection with wide margins (4–8 cm), and serosal patching of anastomosis, the colon is more prone to dehiscence than the small intestine. Pubic and/or ischial osteotomy is possible for malignant lesions in the caudal colon (Yoon and Mann 2008), assess/biopsy regional and mesenteric lymph nodes and liver, adjuvant doxorubicin chemotherapy in cats with colonic ADC (Slawienski et al. 1997); intracavitary chemotherapy for carcinomatosis can extend ST (Moore et al. 1991a; Charney et al. 2005); adjuvant doxorubicin chemotherapy in dogs (Paoloni et al. 2002); feline large intestinal ADC more commonly associated with mucosal ulceration and bowel thickening than annular stenosis (Patnaik et al. 1976). Rectal: surgical approaches: rectal eversion, rectal pull‐through, or resection and end‐to‐end anastomosis, fecal incontinence is uncommon if rectal resection <4–6 cm but fecal incontinence and incisional dehiscence are more common if > 4–6 cm rectum is resected with rectal pull‐through surgery, however, the size of the dog plays a role in how much rectum can be resected (Nucci et al. 2014). Resection via an anal approach (and rectal prolapse) was reported in 22 dogs (Danova et al. 2006). Thoracoabdominal stapling devices were used to resect masses of the distal third of the rectum (in combination with rectal prolapse), with a minimum of 0.5–1 cm margins. Meantime to veterinarian follow‐up was 564 days, and no dog had recurrence of disease during this time (Swiderski and Withrow 2009). Transanal endoscopic resection of benign rectal tumors has been described (Holt and Durdey 1999; Holt 2007; Coleman et al. 2014). In another study, 11 dogs were treated with full‐thickness colorectal amputation by either simple transanal or combined abdominal‐transanal pull‐through technique for colorectal carcinoma, two dogs that had a combined abdominal‐transanal approach died within 4 days (Morello et al. 2008). Incontinent end‐on colostomy has been described in the management of 1 dog with rectal ADC (Kumagai et al. 2003). Piroxicam palliative for rectal tubulopapillary polyps if unresectable or as an alternative to surgery (Knottenbelt et al. 2000). No effective chemotherapy for ADC, but combination of 5‐fluorouracil and cisplatin may be effective (Stanclift and Gilson 2004). Mean survival time 22 months following surgery, radical surgery associated with high complication rate and poor survival (<1 week), local appearance may be predictive of survival: mean ST 32 months if pedunculated, 12 months if nodular or cobblestone, 1.6 months if annular, MST 24 months following cryosurgery (Church et al. 1987). Recurrence of clinical signs occurred in 41% of dogs with benign rectal tumors treated with surgery and 18% of rectal polyps underwent malignant transformation (Valerius et al. 1997b). Large polyps (greater than 1 cm in diameter) frequently had marked epithelial atypia and were considered more likely to recur or to become malignant (Seiler 1979). One case of stenting annular rectal adenoma was reported (Culp et al. 2011).
Anal Sac Adenocarcinoma (ASAC)
Wide local resection for the primary tumor is usually not possible due to location, recurrent disease is difficult to resect, sublumbar lymph nodes can be resected with care, and large node size does not preclude resection. In two studies, death was reported as a result of hemorrhage after debulking of sublumbar lymph nodes (Ross et al. 1991; Bennett et al. 2002). Careful dissection and ligation are required, particularly for invasive/adherent lymph nodes. Aggressive surgery may result in sciatic nerve paresis. Overflow urinary incontinence has also been reported (Ross et al. 1991; Emms 2005). Two of 39 dogs (5%) which underwent removal of sublumbar lymph nodes had intraoperative hemorrhage, which was controlled with a combination of electrocautery and topical hemostatic agents, and transfusion was not needed (Barnes and Demetriou 2017). In another series of dogs, there was an increased complication rate in dogs that had concurrent caudal abdominal lymph node extirpation (n = 8/19, 42%) compared with those that did not (n = 3/55, 5%). Complications included perioperative hemorrhage (n = 4), surgical site seroma formation (n = 3), surgical site dehiscence (n = 3) or herniation (n = 1). Dogs that underwent lymph node extirpation had a MST 422–448 days, while dogs that did not undergo lymph node extirpation had a MST of 529–764 days. However, only dogs that had enlarged lymph nodes were selected for lymph node removal (Potanas et al. 2015; Wouda et al. 2016). Anal sacculectomy alone will often result in failure at sublumbar lymph nodes. Given the high metastatic rate to the sublumbar lymph nodes (40–70%) (Ross et al. 1991; Bennett et al. 2002; Williams et al. 2003; Emms 2005; Potanas et al. 2015; Wouda et al. 2016), and the knowledge that primary tumor size and lymph node metastasis at diagnosis is the two main prognostic factors for canine ASAC (Williams et al. 2003; Polton and Brearley 2007; Potanas et al. 2015; Wouda et al. 2016), there is an argument for removal of sublumbar lymph nodes even if they are not enlarged. Removal of sublumbar lymph nodes prior to enlargement/invasion would logically simplify their surgical removal and would allow for histological staging and prognostication and the need for adjuvant therapy for individual dogs. Radiation therapy can be used either intraoperative for treatment of the sublumbar lymph nodes or post‐operative for both the anal sac ADC and sublumbar lymph nodes. A number of different systemic chemotherapy protocols have been used (Goldschmidt and Zoltowski 1981; Ross et al. 1991; Bennett et al. 2002; Turek et al. 2003; Williams et al. 2003; Emms 2005; Wouda et al. 2016). Benefit of chemotherapy is unknown; platinum drugs have shown 31–33% partial response (Bennett et al. 2002) but did not improve ST in other studies (Polton and Brearley 2007; Potanas et al. 2015; Wouda et al. 2016). Mitoxantrone has been combined with radiation therapy post‐operatively to achieve a MST of 956 days in 15 dogs (Turek et al. 2003), piroxicam has no proven effect but anti‐tumor and anti‐angiogenic effects may be beneficial. Toceranib phosphate (Palladia®) has shown 25% PR for a median duration of 22 weeks, and 62.5% stable disease (SD) for a median duration of 30.5 weeks (London et al. 2012). Dogs with sublumbar lymphadenopathy had a significantly shorter MST (422 days), compared with dogs without lymphadenopathy prior to surgery (529 days) (Potanas et al. 2015). In dogs treated with surgery and adjuvant melphalan chemotherapy the MST in dogs with LN metastasis was 20 months versus 29.3 months for dogs with tumor localized to the anal sac (Emms 2005). MST 544 days in 144 dogs treated with surgery, radiation therapy, chemotherapy, or multimodal treatment and dogs treated with chemotherapy alone had significantly shorter survival (median, 212 days) (Williams et al. 2003). The reported MST for combined surgery, radiation therapy, and chemotherapy is 956 days (Turek et al. 2003). 3D conformal treatment planning resulted in homogenous dose distribution for canine anal sac ADC with lower hot spots and dose ranges, however, greater volumes of surrounding normal structures were irradiated (Keyerleber et al. 2012). Poor prognostic signs include lung ± lymph node metastasis, and treatment, with MST significantly shorter with: lung metastasis (219 days v 584 days) ± any metastasis (16 months v 6 months), dogs not treated with surgery (402 days v 548 days), dogs treated with chemotherapy alone (212 days v 584 days). Williams et al. (2003) and Ross et al. (1991) both reported hypercalcemia to negatively impact survival time, whereas Bennett et al. (2002), Emms (2005), and Potanas et al. (2015) reported no difference in survival time between hypercalcemic and normocalcemic dogs (Ross et al. 1991; Bennett et al. 2002; Williams et al. 2003; Emms 2005; Potanas et al. 2015). Williams et al. (2003) found that dogs with ASACs – 10 cm2 in area had significantly shorter survival times, and Polton and Brearley (2007) found that dogs with tumors > 2.5 cm in length had significantly shorter survival times; however, tumor length of <4.2 cm versus ≥4.2 cm was not a prognostic factor in another study by Potanas et al. (2015) (Williams et al. 2003; Polton and Brearley 2007; Potanas et al. 2015). Cause of death is usually renal failure secondary to hypercalcemia or local or distant metastasis. Repeated surgical removal of metastatic lesions may afford prolonged survival (Hobson et al. 2006; Barnes and Demetriou 2017); debulking and omentalization
disease at surgery, versus 358 days for those with metastatic disease at surgery (Green et al. 2011). Cats with advanced disease (including carcinomatosis) treated with surgery can have long‐term survival (Kosovsky et al. 1988). No proven chemotherapy for ADC, but combination of 5‐fluorouracil and cisplatin may be effective (Stanclift and Gilson 2004), second‐look surgery recommended for evaluation of response to chemotherapy (Stanclift and Gilson 2004). Overall MST in dogs treated with surgical resection was 233 days, sex was a prognostic factor with MST for male dogs 272 days v 28 days for female dogs. In this study, only 2 of 15 dogs received adjuvant chemotherapy (Paoloni et al. 2002). Reported adjuvant chemotherapies in dogs include doxorubicin, carboplatin, gemcitabine, doxorubicin, 9‐aminocamptothecin, cisplatin, and 5‐fluorouracil (Paoloni et al. 2002). Intracavitary chemotherapy for carcinomatosis can extend survival time (ST) (Moore et al. 1991a; Charney et al. 2005). Large intestinal: debilitation and hypoproteinemia may complicate treatment, surgical resection with wide margins (4–8 cm), and serosal patching of anastomosis, the colon is more prone to dehiscence than the small intestine. Pubic and/or ischial osteotomy is possible for malignant lesions in the caudal colon (Yoon and Mann 2008), assess/biopsy regional and mesenteric lymph nodes and liver, adjuvant doxorubicin chemotherapy in cats with colonic ADC (Slawienski et al. 1997); intracavitary chemotherapy for carcinomatosis can extend ST (Moore et al. 1991a; Charney et al. 2005); adjuvant doxorubicin chemotherapy in dogs (Paoloni et al. 2002); feline large intestinal ADC more commonly associated with mucosal ulceration and bowel thickening than annular stenosis (Patnaik et al. 1976). Rectal: surgical approaches: rectal eversion, rectal pull‐through, or resection and end‐to‐end anastomosis, fecal incontinence is uncommon if rectal resection <4–6 cm but fecal incontinence and incisional dehiscence are more common if > 4–6 cm rectum is resected with rectal pull‐through surgery, however, the size of the dog plays a role in how much rectum can be resected (Nucci et al. 2014). Resection via an anal approach (and rectal prolapse) was reported in 22 dogs (Danova et al. 2006). Thoracoabdominal stapling devices were used to resect masses of the distal third of the rectum (in combination with rectal prolapse), with a minimum of 0.5–1 cm margins. Meantime to veterinarian follow‐up was 564 days, and no dog had recurrence of disease during this time (Swiderski and Withrow 2009). Transanal endoscopic resection of benign rectal tumors has been described (Holt and Durdey 1999; Holt 2007; Coleman et al. 2014). In another study, 11 dogs were treated with full‐thickness colorectal amputation by either simple transanal or combined abdominal‐transanal pull‐through technique for colorectal carcinoma, two dogs that had a combined abdominal‐transanal approach died within 4 days (Morello et al. 2008). Incontinent end‐on colostomy has been described in the management of 1 dog with rectal ADC (Kumagai et al. 2003). Piroxicam palliative for rectal tubulopapillary polyps if unresectable or as an alternative to surgery (Knottenbelt et al. 2000). No effective chemotherapy for ADC, but combination of 5‐fluorouracil and cisplatin may be effective (Stanclift and Gilson 2004). Mean survival time 22 months following surgery, radical surgery associated with high complication rate and poor survival (<1 week), local appearance may be predictive of survival: mean ST 32 months if pedunculated, 12 months if nodular or cobblestone, 1.6 months if annular, MST 24 months following cryosurgery (Church et al. 1987). Recurrence of clinical signs occurred in 41% of dogs with benign rectal tumors treated with surgery and 18% of rectal polyps underwent malignant transformation (Valerius et al. 1997b). Large polyps (greater than 1 cm in diameter) frequently had marked epithelial atypia and were considered more likely to recur or to become malignant (Seiler 1979). One case of stenting annular rectal adenoma was reported (Culp et al. 2011).
