Does hCG or hCGβ play a role in cancer cell biology?

The role that hCG might play in the oncogenic process in cancer is certainly complex. We know that the expression of hCG and its beta subunit is a widespread phenomenon which has been described in many cancer subtypes. However, hCG's involvement in breast cancer has been antithetical: the detection of ectopically expressed hCG(β) by breast tumors has been employed as a biomarker of malignancy, and hCG has been proposed as a ligand vehicle for toxic drugs, with the aim of targeting the LH/hCG receptor which is reported to be expressed by malignant breast tissue. However, it has also been proposed that hCG is a protective agent against the development of breast cancer, leading some to advocate hCG administration to non-pregnant women as a prophylactic measure against cancer. Nevertheless, suggestions that hCG is involved in the angiogenesis, metastasis and immune escape that are central to cancer progression - are phenomena which clearly apply to breast cancer. Indeed, a tumor vaccine based upon hCG has very recently been shown to protect against mammary tumors in mice. We propose that this apparent paradox is resolved if the free beta subunit of hCG produced by tumors acts as an autocrine anti-apoptotic and angiogenic growth factor, whilst intact heterodimeric hCG, as in pregnancy, is part of developmental signaling that initiates tissue differentiation (including breast ductal tissue development), and hence reduces the population of stem-like cells which are susceptible to oncogenic factors.