Although one would think the diagnosis of cancer is straightforward, simple and unequivocal, that is often not the case. This presentation will discuss a series of cases where the diagnosis of cancer, or the diagnosis of a non-cancerous process was not obvious. Below is a list of principles to keep in mind as the cases are discussed.

1.  Pets with cancer frequently have diseases other than cancer complicating the diagnosis and management of the tumor.

2.  A complete physical examination and full diagnostic evaluation is necessary to determine the extent of a tumor as well as the extent of the complicating diseases.

3.  Understanding the sensitivity and specificity of a diagnostic test is critical to accurate interpretation of laboratory data.

4.  The presence of a mass does not make a diagnosis of cancer. A biopsy or cytology is necessary to confirm or deny the presence of a neoplastic process.

5.  If a biopsy result does not make sense in the context of the clinical presentation of the pet, review of the tissue by another pathologist or re-biopsy is appropriate.

6.  In pets with cancer, the prognosis of the other diseases present impacts the decision-making process regarding surgery, chemotherapy or radiation therapy for the tumor.

Case 1

"AM" is a 10-year-old male, castrated domestic short hair cat. He was referred for evaluation of a poorly defined mass in his right caudal dorsal lung field on plain radiographs and a second ill defined mass arising from the mediastinum. He had recently experienced weight loss without anorexia, vomiting or diarrhea. Biochemical profile, complete blood count, urinalysis and T4 were normal. FeLV and FIV tests were negative.

Computed tomography of the chest confirmed the presence of two intrathoraic masses.

Case 2

"Scooter" is a 12-year-old female, spayed Schnauzer. She was referred for chemotherapy treatment of a bladder tumor. For the previous 5 months she had exhibited lower urinary tract signs, hematuria, stranguria, pollakiuria. Urinary tract infection with E. coli had been treated with antibiotic, but recurred multiple times. Current therapy for the bladder tumor was piroxicam (Feldene®) and since on this treatment, she had developed bloody diarrhea and anemia. Previous laboratory results included an abnormal Veterinary Bladder Tumor Antigen test, normal thoracic radiographs and biochemical profile. Multiple urinalysis revealed pyuria and hematuria with rod shaped bacteria.

An abdominal ultrasound performed by a board certified radiologist showed a thickened bladder wall.

Case 3

"Sandra" is a 15-year-old female, spayed domestic shorthair cat. She was referred for evaluation of a 1 cm mass between the shoulder blades which had been present for 3-4 months. Cytological evaluation of the mass suggested an injection site sarcoma. Several years ago, she was diagnosed with a heart murmur and receives atenolol (Tenormin®) daily. Sandra has mild renal insufficiency and a urine specific gravity of 1.017.

Three view thoracic radiographs were obtained to determine if pulmonary metastasis were present. The thoracic radiographs were abnormal.

Case 4

"Tiffy" is a 5-year-old female spayed domestic shorthair cat. She was referred for evaluation of non-healing wounds of the face and front paw which had been present for 8 months. The lesions had not responded to antibiotic treatment nor did they resolve when an Elizabethan collar was placed to prevent self-mutilation. Physical examination revealed enlarged submandibular lymph nodes. Thoracic radiographs were normal. Except for a mild neutrophilic leukocytosis, biochemical profile, complete blood count and urinalysis were normal. A biopsy performed by the referring veterinarian showed dermal ulceration and infiltration of the skin by neutrophils and a pleomorphic population of cells. Ulcerative dermatitis was diagnosed.

A pathologist at The Animal Medical Center performed review of the previous biopsy sample.