Is there a benefit to metastatic & primary site RT in RMS w/ persistent marrow disease?

In a patient with high risk rhabdomyosarcoma with significant marrow involvement (Stage IV), who has responded completely on imaging to all known sites after chemo, would you proceed with planned XRT if re-staging bone marrow biopsy still showed rare malignant cells?

2 Answers

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Radiation Oncology · Stanford University School of Medicine

Answered on

While I agree with the response by Dr Ermoian, I believe the case is more complicated than simply irradiating the gross disease at the primary site. Overall survival and Progression Free Survival for Stage 4, Group IV RMS has not changed substantially over the past almost 5 decades, despite many successive cooperative group trials testing new agents added to the gold standard VAC. Chemotherapy alone is not sufficient to sterilize gross disease and/or a large tumor burden. Surgical resection does not play a major role in patients with wide spread metastatic disease, however radiation is effective in providing control to sites of detectable disease that can be localized and irradiated. Thus, I would have a goal to also treat nodal disease and any gross sites of metastatic disease at the time of tumor diagnosis in addition to the primary site. The radiotherapy to metastatic sites may need to be interdigitated between continuing chemotherapy. Although we are told that the patient has had a complete response by imaging, we also know that current techniques of imaging are not useful in predicting outcome. Thus, I would not minimize any planned therapy just because imaging is now negative. Having scattered abnormal cells detected in the bone marrow is also difficult to interpret. In general, random bone marrow aspirate/biopsy under estimate tumor burden and often represent a sampling issue. It may be that functional imaging such as PET will turn out to be a more useful modality to estimate marrow involvement.

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Radiation Oncology · University of Washington Medical Center

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I would treat the primary site based on it likely having the greatest concentration if not burden of disease. However, if for some reason the patient has had a resection with +microscipic margins, then I would be much more hesitant to do local therapy since the burden of disease in that circumstance would not be that different from from the marrow disease. I would be particularly hesitant to do local therapy for microscopic disease in the midst of chemotherapy if the radiation would be expected to be myelosuppressive.