Family physicians and orthopedists rarely see a malignant bone tumor (most bone tumors are benign). The route to osteosarcoma diagnosis usually begins with an X-ray, continues with a combination of scans (CT scan, PET scan, bone scan, MRI) and ends with a surgical biopsy. A characteristic often seen in an X-ray is Codman's triangle, which is basically a subperiosteal lesion formed when the periosteum is raised due to the tumor. Films are suggestive, but bone biopsy is the only definitive method to determine whether a tumor is malignant or benign.

Most times, the early signs of osteosarcoma are caught on X-rays taken during routine dental check-ups. Osteosarcoma frequently develops in the mandible (lower jaw); accordingly, Dentist are trained to look for signs that may suggest osteosarcoma. Even though radiographic findings for this cancer vary greatly, one usually sees a symmetrical widening of the periodontal ligament space. If the dentist has reason to suspects osteosarcoma or another underlying disorder, he or she would refer the patient to an Oral & Maxillofacial surgeon for biopsy. A biopsy of suspected osteosarcoma outside of the facial region should be performed by a qualified orthopedic oncologist. The American Cancer Society states: "Probably in no other cancer is it as important to perform this procedure properly. An improperly performed biopsy may make it difficult to save the affected limb from amputation." It may also metastasise to the lungs, mainly appearing on the chest X-ray as solitary or multiple round nodules most common at the lower regions.

Amputation is the initial treatment, although this alone will not prevent metastasis. Chemotherapy combined with amputation improves the survival time, but most dogs still die within a year. Surgical techniques designed to save the leg (limb-sparing procedures) do not improve the prognosis.

Some current studies indicate osteoclast inhibitors such as alendronate and pamidronate may have beneficial effects on the quality of life by reducing osteolysis, thus reducing the degree of pain, as well as the risk of pathological fractures.

On conventional radiographs, the most common osseous presentation is a permeative lytic lesion with periosteal reaction. The classic description of lamellated or "onion-skin" type periosteal reaction is often associated with this lesion. Plain films add valuable information in the initial evaluation or screening. The wide zone of transition (e.g. permeative) is the most useful plain film characteristic in differentiation of benign versus aggressive or malignant lytic lesions.

Magnetic resonance imaging (MRI) should be routinely used in the work-up of malignant tumors. It will show the full bony and soft tissue extent and relate the tumor to other nearby anatomic structures (e.g. vessels). Gadolinium contrast is not necessary as it does not give additional information over noncontrast studies, though some current researchers argue that dynamic, contrast-enhanced MRI may help determine the amount of necrosis within the tumor, thus help in determining response to treatment prior to surgery.

Computed axial tomography(CT) can also be used to define the extraosseous extent of the tumor, especially in the skull, spine, ribs, and pelvis. Both CT and MRI can be used to follow response to radiation and/or chemotherapy. Bone scintigraphy can also be used to follow tumor response to therapy.

In the group of malignant small round cell tumors which include Ewing's sarcoma, bone lymphoma, and small cell osteosarcoma, the cortex may appear almost normal radiographically, while permeative growth occurs throughout the Haversian channels. These tumours may be accompanied by a large soft-tissue mass while almost no bone destruction is visible. The radiographs frequently do not shown any signs of cortical destruction.

Radiographically, Ewing's sarcoma presents as "moth-eaten" destructive radiolucencies of the medulla and erosion of the cortex with expansion.

Other entities with similar clinical presentations include osteomyelitis, osteosarcoma (especially telangiectatic osteosarcoma), and eosinophilic granuloma. Soft-tissue neoplasms such as pleomorphic undifferentiated sarcoma (malignant fibrous histiocytoma) that erode into adjacent bone may also have a similar appearance.

When diagnosing osteoblastoma, the preliminary radiologic workup should consist of radiography of the site of the patient's pain. However, computed tomography (CT) is often necessary to support clinical and plain radiographic findings suggestive of osteoblastoma and to better define the margins of the lesion for potential surgery. CT scans are best used for the further characterization of the lesion with regard to the presence of a nidus and matrix mineralization. MRI aids in detection of nonspecific reactive marrow and soft tissue edema, and MRI best defines soft tissue extension, although this finding is not typical of osteoblastoma. Bone scintigraphy (bone scan) demonstrates abnormal radiotracer accumulation at the affected site, substantiating clinical suspicion, but this finding is not specific for osteoblastoma. In many patients, biopsy is necessary for confirmation.

On X-ray, giant-cell tumors (GCTs) are lytic/lucent lesions that have an epiphyseal location and grow to the articular surface of the involved bone. Radiologically the tumors may show characteristic 'soap bubble' appearance. They are distinguishable from other bony tumors in that GCTs usually have a nonsclerotic and sharply defined border. About 5% of giant-cell tumors metastasize, usually to a lung, which may be benign metastasis, when the diagnosis of giant-cell tumor is suspected, a chest X-ray or computed tomography may be needed. MRI can be used to assess intramedullary and soft tissue extension.

The diagnosis of giant-cell tumors is based on biopsy findings. The key histomorphologic feature is, as the name of the entity suggests, (multinucleated) giant cells with up to a hundred nuclei that have prominent nucleoli. Surrounding mononuclear and small multinucleated cells have nuclei similar to those in the giant cells; this distinguishes the lesion from other osteogenic lesions which commonly have (benign) osteoclast-type giant cells. Soap-bubble appearance is a characteristic feature.

Regardless of location, all rhabdoid tumours are highly aggressive, have a poor prognosis, and tend to occur in children less than two years of age.

Treatment of bone tumors is highly dependent on the type of tumor.

The first route of treatment in Osteoblastoma is via medical means. Although necessary, radiation therapy (or chemotherapy) is controversial in the treatment of osteoblastoma. Cases of postirradiation sarcoma have been reported after use of these modalities. However, it is possible that the original histologic diagnosis was incorrect and the initial lesion was an osteosarcoma, since histologic differentiation of these two entities can be very difficult.

The alternative means of treatment consists of surgical therapy. The treatment goal is complete surgical excision of the lesion. The type of excision depends on the location of the tumor.

- For stage 1 and 2 lesions, the recommended treatment is extensive intralesional excision, using a high-speed burr. Extensive intralesional resections ideally consist of removal of gross and microscopic tumor and a margin of normal tissue.

- For stage 3 lesions, wide resection is recommended because of the need to remove all tumor-bearing tissue. Wide excision is defined here as the excision of tumor and a circumferential cuff of normal tissue around the entity. This type of complete excision is usually curative for osteoblastoma.

In most patients, radiographic findings are not diagnostic of osteoblastoma; therefore, further imaging is warranted. CT examination performed with the intravenous administration of contrast agent poses a risk of an allergic reaction to contrast material.

The lengthy duration of an MRI examination and a history of claustrophobia in some patients are limiting the use of MRI. Although osteoblastoma demonstrates increased radiotracer accumulation, its appearance is nonspecific, and differentiating these lesions from those due to other causes involving increased radiotracer accumulation in the bone is difficult. Therefore, bone scans are useful only in conjunction with other radiologic studies and are not best used alone.

The histologic diagnosis of malignant rhabdoid tumour depends on identification of characteristic rhabdoid cells—large cells with eccentrically located nuclei and abundant, eosinophilic cytoplasm. However, the histology can be heterogeneous and the diagnosis of MRT can often be difficult. Misclassifications can occur.

In MRTs, the INI1 gene (SMARCB1)on chromosome 22q functions as a classic tumour suppressor gene. Inactivation of INI1 can occur via deletion, mutation, or acquired UPD.

In a recent study, SNP array karyotyping identified deletions or LOH of 22q in 49/51 rhabdoid tumours. Of these, 14 were copy neutral LOH (or acquired UPD), which is detectable by SNP array karyotyping, but not by FISH, cytogenetics, or arrayCGH. MLPA detected a single exon homozygous deletion in one sample that was below the resolution of the SNP array. SNP array karyotyping can be used to distinguish, for example, a medulloblastoma with an isochromosome 17q from a primary rhabdoid tumour with loss of 22q11.2. When indicated, molecular analysis of INI1 using MLPA and direct sequencing may then be employed. Once the tumour-associated changes are found, an analysis of germline DNA from the patient and the parents can be done to rule out an inherited or de novo germline mutation or deletion of INI1, so that appropriate recurrence risk assessments can be made.

The first sign is normally a painless abdominal tumor that can be easily felt by the doctor. An ultrasound scan, computed tomography scan, or MRI scan is done first. A tumor biopsy is not typically performed due to the risk of creating fragments of cancer tissue and seeding the abdomen with malignant cells.

Staging is a standard way to describe the extent of spread of Wilms tumors, and to determine prognosis and treatments. Staging is based on anatomical findings and tumor cells pathology.

Recurrence rate of solid form of tumour is lower than classic form.

Brain imaging (neuroimaging such as CT or MRI) is needed to determine the presence of brain metastases. In particular, contrast-enhanced MRI is the best method of diagnosing brain metastases, though detection is primarily done by CT. Biopsy is often recommended to confirm diagnosis.

The diagnosis of brain metastases typically follows a diagnosis of a systemic cancer. Occasionally, brain metastases will be diagnosed concurrently with a primary tumor or before the primary tumor is found.

The initial evaluation involves radiographs (X-rays) of the affected site, but the only way to confirm the diagnosis is by sampling the tissue via biopsy or needle aspiration.

Sarcomas are given a number of different names based on the type of tissue that they most closely resemble. For example, osteosarcoma resembles bone, chondrosarcoma resembles cartilage, liposarcoma resembles fat, and leiomyosarcoma resembles smooth muscle.

Chemotherapy and radiotherapy are effective in some tumors (such as Ewing's sarcoma) but less so in others (such as chondrosarcoma).

There is a variety of chemotherapy treatment protocols for bone tumors. The protocol with the best reported survival in children and adults is an intra-arterial protocol where tumor response is tracked by serial arteriogram. When tumor response has reached >90% necrosis surgical intervention is planned.

A 2009 revision of the traditional Chompret criteria for screening has been proposed:

A proband who has:

- tumor belonging to the LFS tumor spectrum - soft tissue sarcoma, osteosarcoma, pre-menopausal breast cancer, brain tumor, adrenocortical carcinoma, leukemia or lung bronchoalveolar cancer - before age 46 years;

and at least one of the following:

- at least one first or second degree relative with an LFS tumour (except breast cancer if the proband has breast cancer) before age 56 years or with multiple tumours

- a proband with multiple tumours (except multiple breast tumours), two of which belong to the LFS tumour spectrum and the first of which occurred before age 46 years

- a proband who is diagnosed with adrenocortical carcinoma or choroid plexus tumour, irrespective of family history

Osteochondromas are often asymptomatic and may not cause any kind of discomfort. They are often found accidentally when an X-ray is done for an unrelated reason.

- X-rays are the first tests performed that characterize a lesion. They show a clear picture of dense structures of bones, and will also indicate bone growth pertaining to osteochondroma.

- Computed Tomography (CT) scan can identify the bony lesion in great details and show the presence of calcification. These tests also provide great details, especially in soft tissues with the aide of cross-sectional images.

- Magnetic Resonance Imaging (MRI) is the most accurate method for detecting bone masses in symptomatic cases to depict precise morphology of a tumor. It is used to verify if the palpable mass is continuous with the cortex of the affected bone and to differentiate an osteochondroma from other lesions on the surface of the bone. MRI can also be used to look for cartilage on the surface of tumor and can depict any vascular complications caused by the tumor. An MRI can identify tumors of the spinal column and is often used to diagnose low grade osteosarcoma.

- Ultrasound is done if aneurysms or pseudoaneurysms and venous or arterial thrombosis is suspected. Ultrasound is an accurate method for examining the cartilaginous cap of the osteochondroma. It is also a way of pinpointing bursitis. However, it cannot be used to predict if the growth of tumor is inward in regards to the cap.

- Angiography is used to detect vascular lesions caused by osteochondroma due to ossified cartilaginous cap. It is also used to characterize malignant transformation lesions through neovascularity.

- Clinical testing such as sequence analysis can be done of the entire coding regions of both "EXT1" and "EXT2" to detect mutations.

- A biopsy of the tissue sample of the tumor can also be taken to check for cancer.

Tests for osteochondroma can also identify diseases such as secondary peripheral chondrosarcoma and Multiple osteochondromatosis. In large, secondary chondrosarcoma arises at the site of osteochondroma due to increased thickness of the cartilage cap indicating potential malignant transformation. The symptoms of multiple osteochondromatosis are similar to solitary osteochondroma, but they are often more severe. Painless bumps can arise at the site of tumor and pain and other discomforts can also take place if pressure is put on the soft tissues, nerves, or blood vessels. Dysplasia Epiphysealis Hemimelica (DEH) or Trevor's disease and metachondromatosis (MC) are considered differential diagnosis of both solitary and hereditary osteochondromas. DEH is described as a type of over growth at one or more epiphyses. Similar to osteochondroma, DEH is diagnosed prior to 15 years of age and the growth of lesions end at puberty, when the growth plates close. Metachondromatosis is a rare disorder that exhibit symptoms of both multiple osteochondromas and enchondromas in children and is also inherited in autosomal dominant mode.

Genetic counseling and genetic testing are used to confirm that somebody has this gene mutation. Once such a person is identified, early and regular screenings for cancer are recommended for him or her as people with Li–Fraumeni are likely to develop another primary malignancy at a future time (57% within 30 years of diagnosis).

Following conditions are excluded before diagnosis can be confirmed:

- Unicameral bone cyst

- Giant cell tumor

- Telangiectatic osteosarcoma

- Secondary aneurysmal bone cyst

In addition to being named based on the tissue of origin, sarcomas are also assigned a grade (low, intermediate, or high) based on the presence and frequency of certain cellular and subcellular characteristics associated with malignant biological behavior. Low grade sarcomas are usually treated surgically, although sometimes radiation therapy or chemotherapy are used. Intermediate and high grade sarcomas are more frequently treated with a combination of surgery, chemotherapy and/or radiation therapy. Since higher grade tumors are more likely to undergo metastasis (invasion and spread to locoregional and distant sites), they are treated more aggressively. The recognition that many sarcomas are sensitive to chemotherapy has dramatically improved the survival of patients. For example, in the era before chemotherapy, long-term survival for patients with localized osteosarcoma was only approximately 20%, but now has risen to 60–70%.

Depending on the pet's unique condition, there are several treatment options, including surgery, chemotherapy and radiation therapy. Treating the pain adequately is also of crucial importance to improve the pet's quality of life, especially if amputation is not performed.

Biochemical studies reveal hypophosphatemia (low blood phosphate), elevated alkaline phosphatase and low serum 1, 25 dihydroxyvitamin D levels. Routine laboratory tests do not include serum phosphate levels and this can result in considerable delay in diagnosis. Even when low phosphate is measured, its significance is often overlooked. The next most appropriate test is measurement of urine phosphate levels. If there is inappropriately high urine phosphate (phosphaturia) in the setting of low serum phosphate (hypophosphatemia), there should be a high suspicion for tumor-induced osteomalacia. FGF23 (see below) can be measured to confirm the diagnosis but this test is not widely available.

Once hypophosphatemia and phosphaturia have been identified, a search for the causative tumor should begin. These are small and difficult to define. Gallium-68 DOTA-Octreotate (DOTA-TATE) positron emission tomography (PET) scanning is the best way to locate these tumors. If this scan is not available, other options include Indium-111 Octreotide (Octreoscan) SPECT/CT, whole body CT or MRI imaging.