We found overexpression of CD44+/CD24− in chemoresistance ovarian cancer patients both from flow cytometry blood study and immunohistochemistry study direct from ovarian tissue. CD44+ (cluster of differentiation 44) and CD24− (set of differentiation 24) overexpression is associated with increased ovarian cancer oncogenesis and progression [9, 13]. It is related to metastasizing, recurrence, chemoresistance, and poor survival rates in the ovarian cancer . CD44+ overexpression has also been found in the pancreatic cancer , breast cancer , gastric cancer , urothelial bladder cancer  and colorectal cancer . CD24− is a cell surface adhesion molecule frequently detected in invasive ovarian carcinoma. High CD24− expression in invasive ovarian cancer predicts shorter overall survival than low CD24− markers . CD24− overexpression has been found in many tumours such as ovarian cancer, breast cancer and lung cancer field [21, 22]. Therapeutic blockade and genetic ablation of CD24 resulted in reduced tumour growth in vivo and increased the survival time .
CD44+/CD24− flow cytometry and immunohistochemistry are good predictors of ovarian cancer chemoresistance. We found that the immunohistochemistry CD44+/CD24− AUC value is 0.891 (good accuracy) with significant value (p < 0,05). The sensitivity is 81%, and its specificity is 96% for detecting chemoresistance. Flow cytometry CD44+/CD24− AUC is 0.766 (fair accuracy) with significant value (p < 0,05), with a sensitivity of 78% and specificity of 75%. Flow cytometry and immunohistochemistry of CD44+/CD24− both are proven to be a good predictor of ovarian cancer chemoresistance.
Some of the cancer cells CSCs subpopulations had stem-cell-like properties such as self-renewal capacity, differentiation capacity, aggressiveness, migration, tumorigenesis and chemoresistance. CD44+/CD24− previously well known in has been associated with breast cancer metastasis, chemoresistance and poor prognosis. Meng et al.’s cell lines and cell culture study found that the CD44+/CD24− subpopulation of ovarian cancer also has the characteristics of cancer stem cells. CD44+/CD24− in ovarian cancer correlates with aggressiveness, invasion, migration, tumorigenicity and chemotherapy resistance. Clear cell cancer type of ovarian cancer is an aggressive histology subset, and it showed 99% of CD44+/CD24− while the serous papillary type has 66–77% of CD44+/CD24−. Ovarian cancer with high CD44+/CD24− has shorter median progression-free survival (6 vs 18 months).
Five studies with 417 cases in a meta-analysis study showed that CD44+ protein was associated significantly with poorer cancer-specific survival rates in patients undergoing chemoradiotherapy. CD44 is one of the most common reported markers in many cancers. A study with 83 cases found that CD44v9 expression was linked to a worse 5-years cancer-specific survival . The 5-years survival rate is 29% for the advanced stage of ovarian cancer and 14% for the advanced stage of the colorectal stage. A study by Zhang et al. (2019) found that CD105, CD44+, and CD106 high expression is related to chemoresistance, poorly differentiated cancer cells , invasion properties and chemoresistance . A study from 92 cases of ovarian tumours showed that CD24− expression rate is correlated positively with malignancy, clinical-stage, and metastasis .
A study by Li et al. (2017) found that high CD44+/CD24− in breast tumours related to higher proliferation rates, metastasis, and tumourigenesis. Expression of CD44/CD24 and ALDH1+ were associated with malignancy of different subtypes of breast cancer. A combination of CD44/CD24 has been used to describe the stemness of cancer cells for a long time because a single CSC marker alone was not enough to characterise the stem-cell-like properties of the cancer . Yan et al. (2013) also found that cells with high CD44+/CD24− expression showed higher migration and invasion properties and were the cause of chemoresistance .
Some previous studies also found that CD44+/CD24− is involved in other cancers. High expression of CD44+/CD24− in gastric carcinoma patients can predict a decreased disease-free survival. CD44+/CD24− has a valuable prognostic combination in ovarian cancer, pancreatic cancer, and other solid cancers. Interaction between CD44+/CD24− with osteopontin, epidermal growth factor (EGF), and fibroblast growth factor (FGF) can lead the CSCs to induce self-renewal and promotes cell invasion and metastasis. CD24 high expression has been identified in liver, pancreatic and breast cancer . CD44 and CD24 expression also correlated with lower cancer-specific survival in the urothelial bladder cancer . Expression of CD44 and CD24 was also found both in the membrane and cytoplasm of pancreatic cancer cells. CD44 and CD24 are upregulated in human pancreatic cancer related to the development of pancreatic cancer .
To our knowledge, our study is the first study examining CD44+/CD24− in ovarian cancer directly from the blood by flow cytometry study and from the fresh ovarian cancer tissue by double cocktail immunohistochemistry. However, even though we found strong evidence from both studies that CD44+/CD24− has correlations with ovarian cancer chemoresistance from both studies, we still need further investigations because CD44+/CD24− ovarian cancer phenotype maybe not be the sole cause of the chemoresistance. Advance research is also required to prove that CD44+/CD24− potentially can be used as genetic therapy target for ovarian cancer in the future.