These observations may suggest a potential role for the frequency of PPD-specific IFN-γ secreting cells as a biomarker of successful treatment; Although a review conducted on the use of IFN-γ release assays (IGRA) to monitor infection during chemotherapy previously found variability to preclude use as a biomarker of successful treatment [31], perhaps the assay could be refined and utility improved. The gene discussed is IFNG; the disease is infection.