Labrador cross with mass on antebrachium

Signalment:

7-year-old male neutered Labrador cross

Presenting sign:

7 x 5 cm firm mobile mass on the caudal aspect of the proximal antebrachium, which has grown over the past three months. Otherwise clinically well, with no evidence of lameness and no other history of illness. Physical exam is otherwise within normal limits.

100	Please select an option

1

What would be your next step? Excisional biopsy of the mass Incisional biopsy of the mass using a Tru-Cut biopsy needle under sedation Incisional biopsy, taking a wedge of tissue from the edge of the lesion under general anaesthesia, including a small section of grossly normal tissue, in a way that does not compromise further resection under general anaesthesia. FNA cytology in-house Please select an option Incorrect. This is definitely not the way to proceed. Revise principles of surgical oncology. Incorrect. Not a bad choice, but as the mass is so large and the sample is so small, the sample may be friable and necrotic, leading to difficulty in interpretation, so this should not be your first option. It would be best to perform a fine-needle aspirate (FNA) before histopathology, in case a diagnosis can be reached using cytology only (e.g. lipoma, mast cell tumour, abscess). Incorrect. Correct technique for a histopathological diagnosis, including an idea of behaviour. However, it would be best to perform FNA before histopathology, in case a diagnosis can be reached using cytology only (e.g. lipoma, mast cell tumour, abscess). Correct. It is best to perform FNA before histopathology, in case a diagnosis can be reached using cytology only (e.g. lipoma, mast cell tumour, abscess.) The FNA reveals blood only, but suspicion of sarcoma is increased, as sarcomas do not exfoliate cells readily and it is common to aspirate blood with soft-tissue sarcomas. Abscess and lipoma are ruled out, and a mast cell tumour is unlikely. You proceed to incisional biopsy (technique as described in option 3).

Histopathology report

Gross pathology One pot is submitted:biopsy of the leg. A pece of pale tan resilient tissue measuring 7 x 5 x 5 mm. A representative section is placed in Cassette A. Histopathology This is a section of a tumour composed of sheets of neoplastic pleomorphic polyhedral to spindle cells with a mitotic index approximating 1-2 mitoses per high power field. They are accompanied by minimal collagen. The neoplastic cells have mild karyomegaly and nucleolar prominence together with abundant eosinophilic, vacuolated cytoplasm. Diagnosis Cutaneous soft-tissue sarcoma, grade 2. Comments This diagnosis is in keeping with the previous cytological findings. The minimal collagen and cytoplasmic vacuolation evident in this case raises the possibility of liposarcoma as a more specific diagnosis. In any case, this tumour is likely to be characterized by infiltrative local growth but negligible tendency for metastatic spread.

2

What do you understand about the behaviour of soft-tissue sarcomas (STS)? Locally minimally invasive but generally a high rate of early metastasis Locally minimally invasive and generally a low rate of metastatic disease Locally very invasive and generally a high rate of early metastatic disease Locally very invasive and generally a low rate of metastatic disease Please select an option Incorrect. Review STS before retrying. Incorrect. Review STS before retrying. Incorrect. Review STS before retrying. Correct.

3

What is the metastatic rate of grade 2 STS? Up to 10% Up to 20% Up to 50% Up to 80% Please select an option Incorrect. This is the metastatic rate for low-grade (grade 1) STS. Choose again. Correct. Metastasis tends to occur late in the course of disease. Incorrect. This is the metastatic rate for high-grade (grade 3) STS. Choose again. Incorrect. STS are characterized by a low-to-moderate metastatic rate.

4	What is the metastatic rate of grade 1 STS? Up to 15% Up to 20% Up to 30% Up to 10% Please select an option Incorrect. Choose again. Incorrect. Choose again. Incorrect. Choose again. Correct.

5	What is the metastatic rate of grade 3 STS? Up to 20% Up to 50% Up to 80% Up to 90% Please select an option Incorrect. Choose again. Correct. Incorrect. STS are characterized by a low-to-moderate metastatic rate. Incorrect. STS are characterized by a low-to-moderate metastatic rate.

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