Drugs of interest to pathologists
Drugs related to surgical pathology

Topic Completed: 1 March 2011

Minor changes: 11 December 2020

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PubMed Search: Rituximab [title] "loattrfree full text"[sb] review[ptyp] clinical

Him G. Kwee, M.D.
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Cite this page: Kwee HG. Rituximab. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/drugsrituxan.html. Accessed January 18th, 2021.
Definition / general
  • Chimeric monoclonal IgG1 kappa antibody directed against the CD20 antigen
Trade name
  • Rutixan®
Clinical information
Approved by U.S. Food and Drug Administration for:
  • Previously untreated follicular CD20+ B cell non-Hodgkin lymphoma in combination with first line chemotherapy, in patients achieving complete or partial response to Rituxan in combination with chemotherapy and as a single agent maintenance therapy
  • Nonprogressive (including stable disease) low grade CD20+ B cell non-Hodgkin lymphoma as a single agent after first line CVP chemotherapy
  • Previously untreated diffuse large CD20+ B cell non-Hodgkin lymphoma in combination with CHOP or other anthracycline based chemotherapy regimens
  • Relapsed or refractory low grade or follicular CD20+ B cell non-Hodgkin lymphoma as single agent
  • Previously untreated and previously treated CD20+ chronic lymphocytic leukemia in combination with fludarabine and cyclophosphamide
  • In combination with methotrexate in adults with moderate to severe active rheumatoid arthritis, who have had inadequate response to one or more tumor necrosis factor antagonist therapies
  • In combination with glucocorticoids for adults with granulomatosis with polyangiitis (Wegener's) and microscopic polyangiitis (www.gene.com: Highlights Of Prescribing Information [Accessed 14 December 2018])
  • Cost: 10 mg/ml concentrate 10 ml vial $700 at drugstore.com
Rituxan side effects for pathologists
  • Post-Rituxan loss of CD20 expression is associated with resistance
  • In CLL, it is difficult to evaluate CD20 loss since it is normally expressed only dimly
  • Additional B cell markers may be necessary, such as anti-CD79a, CD19 and PAX5, to detect residual disease; however CD79a antigen is expressed in a wider range of cells than CD20 and is positive in plasma cells
  • CD19 can also be positive in T cell lymphomas
  • After Rituxan therapy, T cell aggregates may be seen in bone marrow; CD3, CD19 or CD79a may be needed to distinguish these nonneoplastic T cell aggregates from residual B cell lymphoma (Appl Immunohistochem Mol Morphol 2009;17:96)
  • Rituxan persists for many months in serum after therapy and is cytotoxic in the presence of complement
  • This condition can cause a positive B cell cytotoxic positive crossmatch in testing for transplantation purposes
  • The human portion of IgG1 in Rituxan is also a target for the antihuman Ig fluorochromes used in flow cytometric crossmatches and could result in a false positive B cell crossmatch
  • Flow and cytotoxic crossmatches can be done if the CD20 is eliminated first with pronase treatment of the cells or if the Rituxan is removed with immununomagnetic bead absorption (Am J Transplant 2006;6:859)
  • The boxed warning of the drug includes the possibility of progressive multifocal leukoencephalopathy as a side effect (www.gene.com: Highlights Of Prescribing Information [Accessed 14 December 2018])
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