This retrospective case-control study was performed on archived formalin-fixed paraffin-embedded tissue samples submitted to NMBU during the period from 1998 to 2015. These samples had been collected for clinical purposes and leftover samples were archived. Owner consent for using leftover samples for research in cancer diseases was given by dog-owners. These samples had been taken for clinical purposes and leftover samples were archived and used for this study.
Inclusion criteria for this study were colorectal tissue from dogs with histologically confirmed colorectal adenoma or adenocarcinoma, and 18 adenoma and five adenocarcinomas were included in addition to nine control samples. Colonic tissue from control dogs were collected at necropsy from dogs euthanized for reasons that did not involve the gastrointestinal tract (n = 9).
Selection of cases and control dogs
For each case, information about the breed, gender, age, histopathological diagnosis, tumour localization, sampling technique and treatment were obtained from the clinical record (Table 1). The dogs with colorectal adenomas and adenocarcinomas were of various breeds represented by both genders and were between 1 and 14 years old, with an average of 8 years. From these dogs, colorectal mucosal samples were collected during surgery (n = 9), colonoscopy (n = 8), or necropsy (n = 2), and in four cases by unknown procedure (Table 1).
Table 1
Overview of dogs and samples
Dog no. | Breed | Gender | Age (y) | Diagnosis* | Tumour location (C/R) | Method of sampling | Treatment |
1 | German shephard | M | 9 | Adeno- carcinoma | R | Surgery | Surgery |
2 | Irish Setter | F | 10 | Adeno- carcinoma | R | Colonoscopy | Surgery |
3 | Shetland sheepdog | M | 14 | Adeno- carcinoma | C | Post mortem | Meloxicam |
4 | English springer spaniel | M | 8 | Adeno- carcinoma | R | Colonoscopy | Piroxicam |
5 | Tibetanian spaniel | M/N | 10 | Adeno- carcinoma | R | Post mortem | Meloxicam |
6 | German shepherd | F | 9 | Adenoma | UN | UN | UN |
7 | Irish Setter | M | 6 | Adenoma | UN | UN | UN |
8 | English setter | M | 8 | Adenoma | UN | UN | UN |
9 | Mixed breed | M | 10 | Adenoma | R | Surgery | UN |
10 | German shephard | M | 4 | Adenoma | R | Surgery | Surgery |
11 | Staffordshire bullterrier | M | 8 | Adenoma | R | Surgery | Surgery |
12 | Papillon | M | 10 | Adenoma | R | Surgery | Surgery |
13 | Colli shorthaired | M | 3 | Adenoma | R | Surgery | Surgery |
14 | Norwegian lundehund | M | 7 | Adenoma | R | Colonoscopy | Surgery |
15 | Cocker spaniel | F | 10 | Adenoma | C | Colonoscopy | no |
16 | Golden retriever | M | 2 | Adenoma | R | Surgery | Surgery |
17 | Bichon havanais | M | 5 | Adenoma | R | Colonoscopy | Surgery |
18 | English setter | M | 11 | Adenoma | R | Surgery | Surgery |
19 | Gordon setter | F | 10 | Adenoma | R | Surgery | Surgery |
20 | Grand danois | M | 10 | Adenoma | C | Colonoscopy | Piroxicam |
21 | Cocker spaniel | M | 12 | Adenoma | C | Colonoscopy | no |
22 | Border collie | F | 12 | Adenoma | R | Colonoscopy | Surgery |
23 | English setter | F | 8 | Adenoma | UN | UN | UN |
24 | West highland white terrier | M | 15 | Respiratory distress | NA | Post mortem | NA |
25 | Miniatur pincher | F | 12 | Lung tumour | NA | Post mortem | NA |
26 | Staffordshire bullterrier | F | 13 | General weakness | NA | Post mortem | NA |
27 | French bulldog | M | 3 | Intervertebral disk hernia | NA | Post mortem | NA |
28 | Alaskan malamute | F | 7 | Polyneuropathy | NA | Post mortem | NA |
39 | French bullldog | F | 3 | Degenerative disk disease | NA | Post mortem | NA |
30 | Collie, longhair | M | UN | Epilepsy | NA | Post mortem | NA |
31 | Pug dog | M | 5 | Urolithiasis | NA | Post mortem | NA |
32 | Chihuahua | M/N | 3 | Multiple fractures, RTA | NA | Post mortem | NA |
*The diagnosis was not determined for all control dogs, thus symptoms/syndromes are described in some of the cases. |
UN, unkown |
NA, not applicable |
RTA, road traffic accident |
The control dogs consisted of various breeds from both genders, and were between 3 and 15 years old, with an average age of 8 years (Table 1).
Tissue samples
Tissue specimens were fixed in 4% neutral buffered formalin, processed routinely, embedded in paraffin wax, cut into 4 µm thick sections and stained with haematoxylin and eosin (HE).
In total, 12 specimens from tumorous tissue were of full thickness, while in 11 specimens, the muscularis mucosae were lacking.
The histopathological diagnoses were evaluated by a board-certified veterinary pathologist (GG), according to the guidelines for classification of canine colorectal adenoma and adenocarcinomas (25). These guidelines suggest that tumours are classified as adenocarcinoma only if neoplastic cells invade muscularis mucosa. Although some of our tumours consisted of cellular features strongly indicating malignancy, they were still classified as adenoma if no invasion of basal lamina was found. (25).
Immunohistochemistry
The following antibodies were used; mouse anti-β-catenin (BD Biosciences, Franklin Lakes, New Jersey), rabbit-anti-CD3 (DAKO, A 0452 North America Inc, California), mouse-anti-dog-CD18 (Leucocyte Antigen Laboratory, California) and anti-Ki67 (Abcam, cat no. ab15580, Cambridge).
The sections were heat treated for antigen retrieval by autoclaving at 121 °C for 15 minutes in 0,01M citric acid pH 6.0 for CD3 and Ki67, and in the microwave in pH 6.6 Target Retrieval Solution (DAKO, Glostrup, Denmark) for CD18 and pH 9.1 tris-EDTA buffer for β-catenin.
Endogenous peroxidase activity was inhibited with blocking reagent for 10 minutes (DAKO Envision system-HRP AEC REF K 4009 for CD3 and 3.0% H2O2 in methanol for Ki67, β-catenin and CD18). Non-specific antigenic sites were blocked with 5% bovine serum albumin (BSA) in Tris-buffered saline (TBS) for CD3, 1% normal goat serum (Vector/Bioteam) in 5% BSA/TBS for Ki67, 2% BSA in TBS for β-catenin and 10% normal goat serum in PBS for CD18. The sections were incubated at room temperature with the following primary antibodies, dilutions and incubation times: rabbit anti-CD3 (60 minutes), rabbit anti-Ki67 (1:1000 in 2,5% BSA/ TBS, 60 minutes), mouse anti-dog-CD18 (1:100 in 10% goat serum, 30 minutes) or mouse anti-ß-catenin (1:2500 in 1% BSA/TBS, 60 minutes). Sections were then incubated for 30 minutes with secondary antibody from the DAKO Envision-kit for CD3, CD18 and ß-catenin, and goat anti rabbit (DAKO, E 432) diluted 1:50 with 2% normal goat serum for Ki67. The Ki67- sections were then incubated for 30 minutes with Elite -ABC- kit (VECTASTAIN PK-6100) at diluted 1:50 in TBS. Colour was revealed for 10 to 15 minutes using DAKO Envision system-HRP AEC for CD3, CD18 and ß-catenin, and the substrate solution (IMMPACT AEC PEROXIDASE SUBSTRATE SK-4205) for Ki67. Between the various steps, the sections were rinsed thoroughly in TBS. Finally, the sections were counterstained with haematoxylin solution for 45 seconds and mounted. Negative control staining was performed by replacing the primary antibodies with non-immunized goat serum, and showed no staining.
Evaluation Of Immunohistochemistry
The sections were blinded and analyzed subjectively. Two pathologists evaluated the IHC score individually and agreed on the final score (CD18 and β-catenin; GG and RR, Ki67 and CD3; GG and ØK). For all sections, the IHC score was determined by evaluating the entire specimen.
For β-catenin, the scoring scheme included prevalence of cells with a positive staining nucleus, using the following grading system: 0: no cells have any positive staining nucleus, 1: <1/3 of the cells have positive staining nucleus, 2: 1/3–2/3 have positive staining nucleus and 3: > 2/3 of the cells have a positive staining nucleus. Furthermore, the intensity of the β-catenin staining in the cytoplasm and the nucleus were scored from 0–3 (no staining, weak staining, moderate staining and strong staining).
The Ki67 staining was considered as nuclear staining in cells, and absence of nuclear staining was considered negative for the antigen. The scoring of Ki67 was only evaluated in the intraepithelial compartment. None of the control samples expressed Ki67, thus the IHC scoring of Ki67 were only reported in tumour samples.
CD3 + cells were defined as clearly stained cytoplasm in the epithelial compartment and within cells in the lamina propria.
For CD3, Ki67 and CD18, a semi-quantitative scoring scheme based on the prevalence of positive staining cells using the following grading system was applied: 0: no staining, 1: few positive cells, 2: a moderate amount of positive cells, and 3: many positive cells throughout the examined tissue.
The scores of the two pathologists were averaged, resulting in one score for each variable. If the difference between the two pathologists deviated by more than one grade (8 out of 228 scores), the slides were reviewed and discussed, resulting in a final score.
Statistical analysis
The IHC score between adenoma and adenocarcinoma were compared, but due to the low number of samples diagnosed as adenocarcinomas, the adenoma and adenocarcinoma were categorized as “tumour samples” when comparing the IHC score to controls. The difference in demographic factors and the IHC score between dogs with adenoma and adenocarcinoma (tumour samples) and control dogs were analysed using non-parametric tests (Wilcoxon test) JMP 14 (SAS, USA). A P-value < 0.05 was considered significant for all statistical tests.