Heat shock protein 70 (Hsp70) is frequently overexpressed in many different tumor types. However, Hsp70 has also been shown to be selectively presented on the plasma membrane of tumor cells, but not normal cells, and this membrane form of Hsp70 (mHsp70) could be considered a universal tumor biomarker. Since viable, mHsp70-positive tumor cells actively release Hsp70 in lipid micro-vesicles, we investigated the utility of Hsp70 in circulation as a universal tumor biomarker and its potential as an early predictive marker of therapeutic failure. We have also evaluated mHsp70 as a target for the isolation and enumeration of circulating tumor cells (CTCs) in patients with different tumor entities. Circulating vesicular Hsp70 levels were measured in the peripheral blood of tumor patients with the compHsp70 ELISA. CTCs were isolated using cmHsp70.1 and EpCAM monoclonal antibody (mAb)-based bead approaches and characterized by immunohistochemistry using cytokeratin and CD45-specific antibodies. In two out of 35 patients exhibiting therapeutic failure two years after initial diagnosis of non-metastatic breast cancer, progressively increasing levels of circulating Hsp70 had already been observed during therapy, whereas levels in patients without subsequent recurrence remained unaltered. With regards to CTC isolation from patients with different tumors, an Hsp70 mAb-based selection system appears superior to an EpCAM mAb-based approach. Extracellular and mHsp70 can therefore serve as a predictive biomarker for therapeutic failure in early-stage tumors and as a target for the isolation of CTCs in various tumor diseases.

Lung cancer remains a devastating disease with a poor clinical outcome. A biomarker signature which could distinguish lung cancer from metastatic disease and detect therapeutic failure would significantly improve patient management and allow for individualized, risk-adjusted therapeutic decisions. In this study, circulating Hsp70 levels were measured using ELISA, and the immunophenotype of the peripheral blood lymphocytes were measured using multiparameter flow cytometry, to identify a predictive biomarker signature for lung cancer patients pre- and post-operatively, in patients with lung metastases and in patients with COPD as an inflammatory lung disease. The lowest Hsp70 concentrations were found in the healthy controls followed by the patients with advanced COPD. Hsp70 levels sequentially increased with an advancing tumor stage and metastatic disease. In the early-recurrence patients, Hsp70 levels started to increase within the first three months after surgery, but remained unaltered in the recurrence-free patients. An early recurrence was associated with a significant drop in B cells and an increase in Tregs, whereas the recurrence-free patients had elevated T and NK cell levels. We conclude that circulating Hsp70 concentrations might have the potential to distinguish lung cancer from metastatic disease, and might be able to predict an advanced tumor stage and early recurrence in lung cancer patients. Further studies with larger patient cohorts and longer follow-up periods are needed to validate Hsp70 and immunophenotypic profiles as predictive biomarker signatures.

The presence of circulating Hsp70 levels and their influence on the immunophenotype of circulating lymphocyte subsets were examined as diagnostic/prognostic biomarkers for the overall survival (OS) in patients with IDH-mutant WHO grade 3 oligodendroglioma, astrocytoma, and IDH-wildtype grade 4 glioblastoma (GBM). Vesicular and free Hsp70 in the plasma/serum was measured using the Hsp70-exo and R&D Systems DuoSet^® Hsp70 ELISAs. The immunophenotype and membrane Hsp70 status was determined by multiparameter flow cytometry on peripheral blood lymphocytes and single-cell suspensions of tumor specimens and cultured cells. Compared to healthy controls, circulating vesicular Hsp70 levels were significantly increased in patients with GBM, concomitant with a significant decrease in the proportion of CD3+/CD4+ helper T cells, whereas the frequency of NK cells was most prominently increased in patients with grade 3 gliomas. Elevated circulating Hsp70 levels and a higher prevalence of activated CD3−/CD56+/CD94+/CD69+ NK cells were associated with an improved OS in grade 3 gliomas, whereas high Hsp70 levels and low CD3+/CD4+ frequencies were associated with an adverse OS in GBM. It is assumed that a reduced membrane Hsp70 density on grade 4 versus grade 3 primary glioma cells and reduced CD3+/CD4+ T cell counts in GBM might drive an immunosuppressive tumor microenvironment.

Background: Liquid biopsy-based biomarkers provide valuable insights into tumor biology, dynamics, burden, relapse prediction and therapeutic responsiveness. The stress-inducible heat shock protein 70 (Hsp70), which is frequently overexpressed in highly aggressive solid tumors and is presented on the cell membrane of tumors but not normal cells, is found in the circulation either as a free protein originating from dying cells or in the context of extracellular vesicles (EVs) that are actively released by viable tumor cells. This study demonstrates the potential value of circulating Hsp70 (eHsp70) levels across multiple solid tumor entities as an entity- and stage-dependent diagnostic biomarker reflecting tumor burden and disease stage. Methods: Circulating eHsp70 levels, as determined using the Hsp70-exo ELISA which detects free and EV-associated Hsp70, in plasma samples collected from patients with different tumor entities (n = 389) prior to the initiation of any oncological therapy and healthy controls (n = 108) between 2021 and 2025, were analyzed retrospectively. Tumor stages were categorized as early, locally advanced, or metastatic. The Kruskal–Wallis test was used for group comparisons and the Receiver Operating Characteristic (ROC) curve was used to evaluate the diagnostic performance of eHsp70 levels. DeLong’s test was used to calculate differences between AUC values. Results: In tumor patients (n = 389), circulating eHsp70 levels were significantly higher than those in healthy controls (n = 108) (Kruskal–Wallis, p < 0.001). eHsp70 levels progressively increased from early-stage to locally advanced and metastatic disease in a stage-dependent manner. Although ROC analysis demonstrated the limited discriminatory performance of eHsp70 levels in early-stage disease (AUC 0.569), increased discrimination was apparent in locally advanced disease (AUC 0.751), metastatic tumors (AUC 0.784) and combined advanced tumor diseases (AUC 0.765; significant by DeLong’s Test comparing early-stage to locally advanced and metastatic tumors), irrespective of the tumor entity with the highest AUC values in metastatic breast cancer (AUC 0.872), sarcoma (AUC 0.861) and non-small cell lung cancer (NSCLC) (AUC 0.835). Apart from minor entity-specific differences, the correlation of eHsp70 levels with the tumor stage remained consistent across all measured tumor entities. Conclusions: Circulating eHsp70 levels are markedly elevated in patients with highly malignant solid tumors and show a consistent, stage-dependent increase across multiple tumor types. These findings suggest that circulating eHsp70, as an indicator of tumor-associated cellular stress and overall tumor burden, represents a valuable biomarker for assessing disease stage, monitoring disease progression, and evaluating therapeutic responses.

Objectives/Background: Heat shock protein 70 (Hsp70) is frequently overexpressed and released from malignant tumors and is associated with tumor aggressiveness and resistance to treatment. While elevated levels of extracellular Hsp70 (eHsp70) in the blood have been associated with unfavorable tumor characteristics, its prognostic significance in the context of long-term follow-up has not yet been sufficiently analyzed. The primary objective of this study was to investigate the prognostic association between preoperative circulating eHsp70 levels and subsequent event-free survival (EFS) in patients with NSCLC undergoing thoracic surgery. Patients with pulmonary metastases from other primary tumors were analyzed as an exploratory subgroup. Methods: The association between eHsp70 levels, clinical outcome, and event-free survival in patients with malignant thoracic diseases was investigated in a retrospective study. Results: A total of 76 patients undergoing thoracic surgery for non-small cell lung cancer (NSCLC) or pulmonary metastases from other primary tumors were included and subsequently followed for disease progression, metastasis, or death. Preoperative eHsp70 levels were significantly higher in patients who experienced an adverse clinical event than in event-free patients (median 194.3 ng/mL [IQR 19.9–493.0] vs. 27.8 ng/mL [IQR 14.3–53.4], p = 0.0064). ROC analysis showed moderate discriminatory performance in the overall cohort (AUC 0.68, 95% CI 0.55–0.81), with an AUC of 0.72 (95% CI 0.56–0.88) in patients with NSCLC and 0.59 (95% CI 0.34–0.83) in patients with pulmonary metastases. In patients with NSCLC, elevated preoperative eHsp70 levels were associated with significantly shorter event-free survival (log-rank p < 0.0001). In multivariable Cox regression analysis restricted to patients with NSCLC, eHsp70 remained independently associated with shorter event-free survival after adjustment for tumor stage, age, and sex (HR 1.33, 95% CI 1.07–1.65, p = 0.010). Conclusions: These findings suggest that circulating eHsp70 may have prognostic relevance in patients with NSCLC. However, prospective validation in larger and independent cohorts is required before its clinical utility can be established.