Clinical history

Simba, 9 year old male intact domestic shorthair cat, presented with firm rapidly growing large subcutaneous ulcerated mass on the inguinal area.  The ventral abdominal haired skin containing a portion of the inguinal mass and the inguinal lymph node are submitted for histopathology.

Histology

The dermis and the subcutis are markedly expanded by a moderately cellular neoplasm. Neoplastic cells are either forming anastomosing poorly-organised vascular spaces and channels, supported by a collagenous stroma, or are arranged in streams and sheets, closely packed, supported by a delicate fibrovascular stroma (Fig. 1 and 2). Neoplastic cells are elongated to spindle-shaped, with a prominent ovoid nucleus and small amphophilic nucleoli, and show moderate anisocytosis and anisokaryosis. Ten mitotic figures are observed in 2.37 mm2 – equivalent to 10 high power (x400) fields.

This neoplasm has metastasized to the inguinal lymph node (Fig. 3).

Figure 1: Haired skin. The dermis and the subcutis are effaced by a malignant vascular neoplasm, consistent with angiosarcoma (Haematoxylin and eosin stain, 5x).

Figure 2: Haired skin. Higher magnification of the angiosarcoma. Note the anastomosing poorly-organised vascular spaces (clear spaces, highlighted with asterisks), lined by a single layer of endothelium and  supported by a collagenous stroma (pink areas) (HE stain, 10x).

Figure 3: Inguinal lymph node. The nodal architecture is effaced by a metastatic angiosarcoma (HE stain, 10x).

Interpretation
Angiosarcoma, with nodal metastasis: ventral abdominal haired skin and inguinal lymph node.

Comments
Histology of the ventral abdominal haired skin submitted captures a malignant vascular neoplasm, consistent with angiosarcoma. In this particular case, this angiosarcoma has metastasised to the inguinal lymph node.

Angiosarcoma is a general term for a highly malignant neoplasm arising from endothelial cells of blood vessels (haemangiosarcoma) or lymphatic vessels (lymphangiosarcoma). If the neoplastic vascular channels are filled with blood, this would provide further evidence supporting a diagnosis of haemangiosarcoma. However, immunohistochemistry using endothelial cell markers (factor VIII and CD31) and  a lymphatic vessel marker (PROX-1) may be necessary to further characterise the neoplastic cells and determine whether the angiosarcoma represents a haemangiosarcoma or a lymphangiosarcoma. It should be noted, however, that it is currently unknown whether the different phenotypes affect treatment response or prognosis.

Angiosarcoma is rare in cats; however, the most commonly reported primary sites are cutaneous and visceral locations. Angiosarcomas in cats show a predilection for the subcutis of the caudal ventral abdominal wall, as observed in this case, and this condition is known as ‘feline ventral abdominal wall angiosarcoma’ (FVAA).

FVAA primarily affects middle-aged to older cats, with no distinct breed or gender predisposition.  Clinically, it manifests as a rapidly enlarging, firm to soft mass located in the ventral abdominal region. The mass may appear subcutaneous or involve deeper tissues, such as the abdominal musculature, and is prone to ulceration or spontaneous bleeding due to its vascular nature. Some patients  may present with lesions resembling bruising or inguinal hernia, which may not initially raise suspicion of a neoplastic process.

In addition to the mass, affected cats may present with non-specific clinical signs such as lethargy, anorexia, weight loss, and general malaise. If the neoplasm has metastasised or invaded adjacent structures, clinical signs can include respiratory distress (if pulmonary metastases are present), pale mucous membranes (due to internal haemorrhage), or abdominal distension.

Diagnosis of FVAA typically involves a thorough clinical examination, coupled with imaging studies such as ultrasound or radiography to evaluate the extent of the mass and to check for signs of metastasis. Fine-needle aspiration or core biopsy of the mass may provide initial cytological findings, often showing spindle-shaped or pleomorphic cells with abundant mitotic activity. However, cytology alone may not be definitive due to the poorly exfoliative nature of the cells, and histopathology is ultimately needed to diagnose this condition.

The prognosis for cats diagnosed with ventral abdominal wall angiosarcoma is generally guarded to poor, due to the highly aggressive and invasive nature of the tumour. Angiosarcomas have a marked propensity for local recurrence, even after seemingly complete surgical excision, and a high likelihood of metastasis. The lungs and liver are the most common sites of metastasis, but the tumour can also spread to other organs, including the spleen and kidneys.

Surgical resection is the primary treatment option, and wide surgical margins are essential to reduce the risk of recurrence. However, achieving complete excision can be difficult due to the tumour’s infiltrative growth pattern. Even with aggressive surgical intervention, recurrence rates are high, and the median survival time post-surgery is often limited to a few months. In cases where metastasis has already occurred at the time of diagnosis, survival time may be significantly shorter.

Overall, while early detection and aggressive surgical management may provide temporary control of the disease, the long-term outlook for cats with ventral abdominal wall angiosarcoma remains poor, and most cases have a guarded prognosis. Owners should be informed of the tumour’s aggressive behaviour and potential for rapid progression, and monitoring for recurrence is essential post-surgery.

Reference

Bellamy E, Larsen Moberg H, Suárez-Bonnet A, Palma SD, Murgia D, Pittaway R, Verganti S. Feline ventral abdominal wall angiosarcoma: haemangiosarcoma or lymphangiosarcoma? Clinical and pathological characteristics in nine cases. J Feline Med Surg. 2024 Jan;26(1):1098612X231216636. doi: 10.1177/1098612X231216636. PMID: 38227337; PMCID: PMC10949878.