Page 383 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

CHAPTER 19 Tumors of the Skin and Subcutaneous Tissues 361

invasion, including through the cartilage of the ear canal, can Several prognostic factors have been identified for ceruminous
occur. Advanced imaging (CT or MRI) is indicated to better gland adenocarcinomas (Table 19.4). In cats a proposed grading
scheme was not prognostic for survival, but a mitotic index ≤2
delineate the extent of local disease before surgery. Skull radio-
VetBooks.ir graphs revealed lysis of the bulla in 13 of 27 dogs with malig- predicted improved survival. 160 A correlation between mitotic
index and tumor grade was also noted in a series of cats and dogs
nant tumors of the ear canal, and sclerosis of the bulla was
evident in eight dogs. 154 LN and distant metastasis are uncom- treated with RT, although the small sample size precluded further
mon, with LN metastasis diagnosed cytologically in 1 of 30 evaluation for prognostic significance. 157 The overriding conclu-
dogs and pulmonary metastasis in 3 of 35 dogs, in addition sion from the series of studies regarding treatment for ceruminous
to one dog with a lytic bone lesion. 154 In cats with malignant gland adenocarcinoma is that, with appropriate local therapy,
ceruminous gland adenocarcinomas, 5 of 27 cats had lysis of long-term survival is possible.
the bulla on skull radiographs, and five cats had sclerosis of the
bulla. 154 Five of 56 cats had cytologic evidence of regional LN Tumors of the Digit
metastasis, but none of 32 cats evaluated had evidence of dis-
tant metastasis. 154 A staging scheme adopted from the human The most common malignant digit tumors of dogs include SCC
ear canal tumors has been proposed for primary tumors of the (47%), melanoma (24%), STS (13%), MCT (8%), osteosarcoma
ear canal in cats and dogs (Table 19.3). 157 (OSA, 3%), round cell sarcoma, adenocarcinoma, malignant adnexal
Surgery is recommended for excision of noninvasive ear tumor, HSA, lymphoma, chondrosarcoma, giant cell tumor of bone,
canal tumors; total ear canal ablation and lateral bulla oste- and synovial cell sarcoma. Benign and nonneoplastic diseases of the
otomy (TECA-LBO) is most commonly indicated. 158,159 Local canine digits include pyogranulomatous inflammation, epithelial
tumor recurrence was significantly decreased in both dogs and inclusion cysts, IKA, benign adnexal tumors, histiocytoma, hem-
cats treated with TECA-LBO compared with those treated angioma, BCT, intraosseous epidermoid cyst, infiltrating lipoma,
with a lateral ear canal resection. 158,159 The MST for cats and fibroma, papilloma, hamartoma, trichoblastoma, keratoma, and
dogs with malignant ear canal tumors treated with TECA- plasmacytoma. 161,162 The median age at diagnosis is 10 years. 161,163
LBO was 42 to 50.3 months and not reached at 36 months, Approximately 3% of dogs with digital SCC have involvement of
respectively. 158–160 RT also appears effective for the treatment multiple digits. These dogs are typically large breed dogs with a black
of ceruminous gland adenocarcinoma 157 ; six cats and five dogs hair coat. 164,165 Predisposed breeds for multiple digit SCCs include
treated with orthovoltage RT (12 4-Gy fractions for a total standard poodles, black Labrador retrievers, giant schnauzers, Gor-
165
dose of 48 Gy) had an estimated mean PFS of 39.5 months and don setters, rottweilers, Beaucerons, and Briards. Additional breeds
a 1-year PFS rate of 56%. that may be predisposed to digital SCC include dachshunds and flat-
162
coated retrievers. The thoracic limbs are more commonly affected
165
than the pelvic limbs. Scottish terriers were overrepresented in dogs
with digital malignant melanomas. 162
Proposed Staging Scheme for Primary
TABLE 19.3 The definitive diagnosis of a digital mass can be difficult in
Tumors of the Ear Canal 165 both cats and dogs. A review of pathologists demonstrated a 20%
T 1 Tumor confined to the external or horizontal ear canal rate of disagreement in the diagnosis of digital tumors, with 75%
of the changes in diagnosis being clinically significant. 166 The dif-
T 2 Tumor extending beyond the tympanic membrane ferentiation between SCC and IKA was most difficult.
T 3 Tumor extending beyond the middle ear/bone destruction The most common digital tumors in cats include SCC (25%),
fibrosarcoma (23%), adenocarcinoma (22%), OSA (8%), HSA

TABLE 19.4 Prognostic Factors for Primary Tumors of the Ear Canal
Prognostic Factor Species Median Survival (Months) Reference
Mitoses per high power field ≤2 Feline ≈180 160
≥3 ≈24
Extension beyond the ear canal No Canine 30 154
Yes 5.9
Presence of neurologic signs No Feline 15.5 154
Yes 1.5
Histology Ceruminous gland adenocarcinoma Feline 49 154
Squamous cell carcinoma 3.8
Carcinoma of unknown origin 5.7
Extension beyond the ear canal No Feline 21.7 154
Yes 4