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NBME 18 Answers

nbme18/Block 1/Question#19 (reveal difficulty score)
70 yo woman, increasingly severe pain in ...
Pleomorphic neoplastic cells producing new woven bone ๐Ÿ” / ๐Ÿ“บ / ๐ŸŒณ / ๐Ÿ“–

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submitted by mahesh(7)

Osteosarcoma histological appearance. Paget disease is one of risk factor

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spow  Looking back, I know it's osteosarcoma but the lung metastases made me think of Ewing's +
makinallkindzofgainz  Ewing sarcoma is common in boys <15 years old. This patient is a 70 year old woman. The stem notes elevated periosteum and a sunburst pattern which are characteristic of osteosarcoma. +2
llamastep1  Also "sunburst pattern" is a classic description of Osteosarcoma. +1

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submitted by โˆ—mamed(25)

What is the neoplastic chondrocytes filling lacunes?

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mumenrider4ever  I think that's a chondrosarcoma (tumor of malignant chondrocytes, found in the pelvis, proximal femur and humerus, FA 2020 pg. 465) +1

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submitted by โˆ—windy48(0)
  • Although rare in the elderly,"sunburst" pattern is the textbook presentation of osteosarcoma.

  • The answer is almost verbatim from FA: "Pleiomorphic osteoid-producing cells (malignant osteoblasts)."

  • Paget's disease is a risk factor for osteosarcoma

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submitted by โˆ—step7777(7)

Of note, osteosarcoma also is the only bone tumor with a biphasic epidemiological distribution. More common in adolescents, but can also occur in elderly.

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drdoom  also known as โ€œbimodalโ€ (since distribution shows two modes: in the second decade of life and the eighth) +

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submitted by saraluciachega(1)

Also, remember that Paget disease increases risk of osteosarcoma (seen in histology as neoplastic spindle-shaped stromal cells admixed with tumor osteoid and thin trabeculated bone)

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