Lifespan and Causes of Death in the Irish Wolfhound - Vetsuisse ...

2002). On the molecular level, the forming of cancer is a multi-step process involving
DNA damage (either inherited or environmental), expression of growth promoters
(pre-cancerous phase) and finally accumulation of further genetic changes, leading to
increased malignancy (Ruttemann 2005).
OS cells are poorly differentiated, mesenchymal in nature and produce osteoid, bone
substance and, occasionally, cartilaginous tissue. The tumour is characterised by an
aggressive local osteolysis, periosteal reaction with the formation of new bone tissue
and more or less pronounced soft tissue swelling. Micro-metastases occur early in
the course of the disease; the most common sites being the lungs and other bones.
Over 90% of affected individuals may have microscopic lung metastases at the time
of diagnosis (Chun and Morrison 2004). Osteolysis can eventually lead to
pathological fractures of the affected bone (Suter and Niemand 2001 b).
3.4.1.2 Symptoms
OS can remain without symptoms for some time and then gradually or suddenly
cause various degrees of lameness, the development of which can be combined with
an actual or perceived injury to the limb in question. Symptoms of manifest OS
include lameness and strong pain upon palpation. A swelling is not obligatory and
usually only easily discernable where the bone is not covered by muscle (Suter and
Niemand 2001 b). The most frequent locations are reported to be “distant from the
elbow, close to the knee” (Chun and Morrison 2004).
3.4.1.3 Diagnosis
Every metaphysical swelling in middle-aged large dogs should be considered
potentially tumorous until the assumption is disproved (Suter and Niemand 2001 b).
Radiographic signs include a combination of bone lysis and proliferation, which can
lead to the characteristic “sunburst” pattern (Kramer, Latimer et al. 2003). As
opposed to benign changes (osteomyelitis), there is no sclerotic demarcation line
between the lesion and healthy bone tissue. Marked soft tissue swelling is also
common (Suter and Niemand 2001 b; Chun and Morrison 2004).
Pulmonary metastases are often invisible at the time of diagnosis, but as stated
above, it is very probable that micro-metastases are already present in dogs with
manifest clinical signs of OS despite this. Nevertheless, thoracic radiographs (3
views) should always been taken when OS is suspected (Chun and Morrison 2004).
It is also possible, although unusual, to additionally do CT or scintigraphic bone
scans to diagnose OS. CT is more sensitive at detecting early bone lysis, while
scintigraphy may be useful for identifying metastatic disease at an earlier stage than
X-rays. The latter procedure will not distinguish between sites of previous trauma or
inflammation and metastases though (Chun and Morrison 2004).
Laboratory findings are absent or non-specific, but it seems that an increased AP
level is associated with a poorer prognosis (Chun and Morrison 2004).
The gold standard for diagnosis is a tumour biopsy. Given that different tumour types
react differently to different therapy protocols and have varying prognoses, it should
be considered if a specific therapy is planned. Multiple core biopsies using a
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