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WASHINGTON -- Though seemingly rare, osteosarcoma can masquerade as a sports-related injury, a physician said at the American Academy of Pediatrics annual meeting.

In fact, osteosarcomas account for 3% of all childhood cancers and are the most common type of bone cancer, Haley Powell, DO, of Children's Hospital of Philadelphia, noted in a case series of three teen patients.

Osteosarcoma mainly affects the long bones in adolescents. Initial symptoms, like joint pain, swelling, or limp, can be vague, which is why a thorough evaluation and appropriate workup is critical for diagnosis, Powell said.

The case series consisted of three patients: a 17-year-old female wakeboarder, a 17-year-old male theater student, and a 16-year-old female dancer.

The wakeboarder presented with gradual knee and thigh pain that progressively worsened over the course of 8 weeks. The pain was mostly at rest. A patient exam did not reveal tenderness to palpation or limited range of motion, but there was slight weakness from atrophy.

X-rays were obtained for the patient, and imaging showed that, in the distal femur, there was significant heterogeneity in the bone itself, "which is concerning for bone marrow involvement," Powell said. An MRI then showed a mass in the distal femur, also affecting the soft tissue structures around the humerus.

The teen was treated by hematology/oncology services "after seeing us in sports medicine," Powell said, and she is now in remission.

The theater student reported worsening of knee and calf pain as well as swelling for 4 weeks following an injury while performing choreography. The teen's pain was primarily with ambulation. An exam revealed pain over the medial joint line, a positive lateral McMurray test, limited flexion and extension, and a positive Apley's test.

In this case, the patient's x-ray was not extremely concerning, Powell said. "You have to really be looking hard, but on the patient's right leg on the medial condyle of the distal femur there's some heterogeneity inside the bone itself and maybe a little bit of periosteal irregularity...as well, but very difficult to see."

An MRI was already in the works because of meniscal concerns, however the imaging revealed a giant mass instead. Importantly, this case "shows that these can present as traumatic cases too," she noted. "They can have a mechanism of injury, but they're really osteosarcoma."

She said the patient had an amputation, and no metastasis.

The dancer reported gradual knee pan and limpness for 6 weeks that was worse with bending and walking up stairs. But the teen also noted that her knee hurt all the time.

A year prior to the presentation, the patient's contralateral knee pain was diagnosed as patellofemoral syndrome. She had tenderness to palpation over the lateral joint line and posterior aspect of the knee, limited flexion and extension, and positive patellar grind. There was no palpable mass.

Notably, despite the latter observation, on the patient's x-ray, Powell noted there was a "very obvious mass." Imaging revealed a bony mass on the posterior aspect of the distal femur.

The patient had multiple lung relapses, she said, and passed away at the age of 25 earlier this year.

Powell pointed out that it was important to note that, though all three patients presented to a sports medicine clinic, their underlying etiology was oncologic.

Many athletes first report to their primary care provider seeking an initial diagnosis and subsequent guidance, she noted. Significantly, in all three cases, the adolescents had worsening pain that lasted 4 to 8 weeks and that occurred at rest.

It's important to "keep in mind the patient's chronicity of pain, the location of their pain, their age," Powell pointed out. These factors play a role in determining the urgency of an x-ray, for instance.

"We just wanted to bring the recognition, the nuances of osteosarcomas, and how they can present to any clinical setting, really," she said.

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