The ability of MSOT to follow tumor growth and the treatment response in murine xenograft models by specifically discriminating and determining oxygenated (HbO2) and deoxygenated hemoglobin (Hb) within the hypoxic TME has recently been shown by Karlas et al. [24] and Quiros-Gonzalez et al. [25]. The gene discussed is GSTM1; the disease is neoplasm.