As the values measured with the compHsp70 ELISA were more than 100-fold higher compared to those measured with the R&D Systems Hsp70 ELISA (median compHsp70 ELISA: 674.32 ng/mL; median R&D Hsp70 ELISA: 4.78 ng/mL), we assume that in malignant neoplasia such as osteosarcoma, predominantly exosomal Hsp70 derived from viable tumor cells contribute to the elevated Hsp70 levels. The gene discussed is HSPA1A; the disease is osteosarcoma.