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

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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.

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Review the histopathology report. 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.

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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.

6

What would you choose to do next? a) Abdominal ultrasound for staging purposes b) Thoracic radiographs for staging purposes c) Bone marrow biopsy for staging purposes d) Palpation of regional lymph node and FNA of this lymph node if enlarged. e) Options b) and d) Please select an option Incorrect. Although this is reasonable to check for intercurrent disease, it is unlikely that a grade 2 STS would metastasize to intra-abdominal organs so not your next choice. This option is more appropriate for high-grade or anaplastic STS. This is correct but there is a better option. This is the commonest site for metastatic disease for STS. However, you should also assess your regional lymph nodes, as in option e. This is of little or no value in this case. This is also correct as STS can metastasize to regional lymph nodes. You should try and demonstrate evidence of metastasis with FNA before surgery, as this may change the prognosis and thus the client’s willingness to treat. However, cytology of regional lymph nodes may not be adequate for staging and histopathology is better to prove lymph node metastasis. It is important to remove enlarged regional lymph nodes at the time of surgery and send for histopathology just to be sure. You should also take thoracic radiographs for staging purposes, as lung is the most common site for metastasis of STS. Choose again. Correct. This is the best answer.]]

7

You now know that the regional lymph node is not palpable, and the thoracic radiographs are unremarkable. You have adequately staged this tumour to stage I (primary site only). What can be expected with adequate treatment of this tumour? Extension in survival time is possible, but a cure is unlikely A cure is likely with adequate treatment. Please select an option Incorrect. Review STS before retrying. Correct.

8

Haematology, biochemistry and urinalysis before surgery are within normal limits. What is your preferred option for treatment of the local tumour? Amputation alone OR chemotherapy alone Marginal excision with adjuvant radiation therapy OR excision with widest margins possible and reconstruction with a skin flap Amputation OR marginal excision with adjuvant radiation therapy Radiation therapy alone OR amputation Chemotherapy alone OR marginal excision alone Please select an option Incorrect. Amputation is a valid treatment option, as wide margins without amputation will be difficult to guarantee with the size of the tumour and its location. However, STS is minimally, if at all, responsive to chemotherapy. Choose again. Incorrect. Marginal excision with adjuvant radiation therapy is expected to provide long-term control of local disease, with 70% of local STS of all grades controlled for at least 1 year. However, excision with widest margins possible and reconstruction with a skin flap is not a preferred treatment option, as wide margins without amputation will be difficult to guarantee with the size of the tumour and its location. However, if radiation therapy is not available and the clients refuse amputation, this could be tried and may give favourable results if margins prove to be clean. Choose again. Correct. These are the two best options to achieve cure or long-term control. Incorrect. STS as gross, large-volume disease is minimally responsive to radiation, so this should not be a preferred option. This dog could be cured! However, amputation is a valid treatment option, as wide margins without amputation will be difficult to guarantee with the size of the tumour and its location. Choose again. Incorrect. STS is minimally, if at all, responsive to chemotherapy. Marginal excision alone is also not a preferred treatment option as local recurrence is expected within 1 year in 60% of cases. Choose again.

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