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NBME 18 Answers

nbme18/Block 1/Question#19 (16.2 difficulty score)
70 yo woman, increasingly severe pain in ...
Pleomorphic neoplastic cells producing new woven bone🔍

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submitted by mahesh(5),
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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. +1  
llamastep1  Also "sunburst pattern" is a classic description of Osteosarcoma. +  

submitted by mamed(14),

What is the neoplastic chondrocytes filling lacunes?

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

submitted by 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

submitted by step7777(0),

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

drdoom  also known as “bimodal” (since distribution shows two modes: in the second decade of life and the eighth) +