Fibroma

Fibroma

A benign tumor of mature fibrocytes producing abundant collagen.

Gross Appearance:
•Uncommonly, the tumors may be found as pedunculated, soft growths of the skin (fibroma molle-soft)
•More commonly cases present as firm intradermal and subcutaneous masses (fibroma durum-hard)
•Present in the dermis and may extend into the subcutaneous tissue, or may only be present within the subcutaneous tissue.
•Most appear well circumscribed
•Range in size from 1 to 5 cm in diameter
•On cut section the tumor has a gray to white appearance
•An interwoven pattern to the tissue is often discernible on careful examination
•This tumor occurs in the dog, but not in the cat

Histology:
•Elongate spindle-shaped cells
•Abundant collagenous stroma
•Cells are uniform
•Little to no nuclear atypia or hyperchromasia
•Nuclei and collagen fibers are arranged in ill-defined interwoven bundles
•Occasionally, collagen within fibromas appears thick, glassy and brightly eosinophilic, as may be seen in keloids

Breeds At Increased Risk
Breed	Odds Ratio	95% Confidence Limit	Probability
Rhodesian Ridgeback	3.25	1.87 - 5.65	0.001
Doberman Pinscher	2.54	2.14 - 3.02	0.001
Brittany	1.95	1.25 - 3.04	0.007
Rottweiler	1.71	1.32 - 2.21	0.001
Dalmatian	1.70	1.10 - 2.62	0.022
Boxer	1.65	1.31 - 2.09	0.001
Great Dane	1.65	1.08 - 2.53	0.027
Golden Retriever	1.41	1.20 - 1.65	0.001
German Shepherd	1.24	1.01 - 1.52	0.041

Breeds At Decreased Risk
Breed	Odds Ratio	95% Confidence Limit	Probability
Lhasa Apso	0.49	0.27 - 0.89	0.013
Irish Setter	0.47	0.24 - 0.95	0.026
Cocker Spaniel	0.43	0.31 - 0.59	0.001
Dachshund	0.39	0.21 - 0.73	0.001
Standard Poodle	0.26	0.12 - 0.58	0.001
Miniature Poodle	0.24	0.14 - 0.41	0.001
West Highland White Terrier	0.16	0.05 - 0.51	0.001
Chihuahua	0.12	0.02 - 0.84	0.004
Yorkshire Terrier	0.04	0.01 - 0.31	0.001

Sex Distribution (N=1360)

Sex Status
Percent

Male
(45.0%)

50.9%

intact
(28.1%)

28.7

neutered
(16.9%)

22.2

Female
(55.0%)

49.1%

intact
(23.9%)

19.2

neutered
(31.1%)

29.9

(normal sex distribution)

Anatomic Location (N=1697)

Site
Percent

Forelimb 22.7

Hindlimb 21.7

Head 15.6

Thorax 12.1

Abdomen 11.3

Multiple 5.2

Neck 3.9

Back 3.1

Tail 1.9

Perineum 1.9

Scrotum 0.6