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Presented by Edward McCarthy, M.D. and prepared by Greg Seidel, M.D.
Case 6: A 40 year old man had pain in his femur for one month.
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1. Question
Week 120: Case 6
A 40 year old man had pain in his femur for one month. A radiograph demonstrated a poorly defined mixed radiolytic and radiodense lesion./images/0113036a.jpg
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/images/0113036c.jpgCorrect
Answer: Primary lymphoma of bone
Histology: Primary malignant lymphomas of bone present as destructive lesions composed of small round blue cells. It is usually impossible to absolutely distinguish between other small round blue cell neoplasms without immunohistochemical stains. Typically, malignant lymphomas in bone are large B-cell lymphomas. Therefore there is strong positivity with CD-20.
Discussion: Ewing’s sarcomas can have similar radiographic patterns and can even occur in patients as old as the present patient. However, Ewing’s sarcomas are positive for CD-99 and are negative for lymphoid markers. Problems arise when the small round blue cell neoplasm is a lymphoblastic lymphoma. Lymphoblastic lymphomas may not have mature lymphoid markers and appear negative for a lymphocyte phenotype. Also problematic is that many lymphoblastic lymphomas are CD-99 positive. Lymphoblastic lymphomas, however, are positive with stains for primitive lymphoid differentiation such as TDT. A positive TDT stain is highly suggestive of a lymphoblastic lymphoma.
Patients in this age group should be suspected for having metastatic carcinoma. Specifically, metastatic small cell carcinoma may masquerade as a small round blue cell neoplasm. However, in this case the distinctive histology of small cell carcinoma is not present. Although stains for keratin in small cell carcinoma may be only focally positive. Also, there is negativity for lymphoid markers and CD99.
The lesion is not multiple myeloma because the cytologic features of plasma cells are not present despite the fact that many lymphomas have an immunoblastic phenotype. The most important differentiating feature is that myeloma cells will stain positive for CD138.
Incorrect
Answer: Primary lymphoma of bone
Histology: Primary malignant lymphomas of bone present as destructive lesions composed of small round blue cells. It is usually impossible to absolutely distinguish between other small round blue cell neoplasms without immunohistochemical stains. Typically, malignant lymphomas in bone are large B-cell lymphomas. Therefore there is strong positivity with CD-20.
Discussion: Ewing’s sarcomas can have similar radiographic patterns and can even occur in patients as old as the present patient. However, Ewing’s sarcomas are positive for CD-99 and are negative for lymphoid markers. Problems arise when the small round blue cell neoplasm is a lymphoblastic lymphoma. Lymphoblastic lymphomas may not have mature lymphoid markers and appear negative for a lymphocyte phenotype. Also problematic is that many lymphoblastic lymphomas are CD-99 positive. Lymphoblastic lymphomas, however, are positive with stains for primitive lymphoid differentiation such as TDT. A positive TDT stain is highly suggestive of a lymphoblastic lymphoma.
Patients in this age group should be suspected for having metastatic carcinoma. Specifically, metastatic small cell carcinoma may masquerade as a small round blue cell neoplasm. However, in this case the distinctive histology of small cell carcinoma is not present. Although stains for keratin in small cell carcinoma may be only focally positive. Also, there is negativity for lymphoid markers and CD99.
The lesion is not multiple myeloma because the cytologic features of plasma cells are not present despite the fact that many lymphomas have an immunoblastic phenotype. The most important differentiating feature is that myeloma cells will stain positive for CD138.