Osteoblasts and osteoclasts: an important switch of tumour cell dormancy during bone metastasis

Table 2 The role of osteoclasts and bone resorption in reactivating dormant tumour cells

Dormant cancer types	Factors that induced bone resorption	Mechanisms	Reference
Prostate and breast cancer cells	PTH stimulation / calcium restriction	↑ tumour development in bone	[39, 40]
Breast cancer cells	Osteoclasts secreted MMP-9	↑ bone angiogenesis and ECM remodelling	[41, 42]
Breast cancer cells	Osteoclasts secreted TGFβ1	↑ a mesenchymal phenotype and motility	[43]
Myeloma cells	Osteoblast expressed sRANKL	Remodelling the endosteal niche	[21]
Breast cancer cells	OVX (surgery)	↓ expression of the osteoblast formation inhibitors Dkk1, 2 and 3; ↑ PTH expression	[44]
ER-positive breast cancer cells	Oestrogen depletion (surgery)	↑ ANGPT2 signalling	[45]
Prostate cancer cells	Androgen deprivation (surgery)	↑ serum levels of the osteoclast marker TRAP and P1NP	[46]

Note: ‘↑’ represents increased, upregulated, induced, enhanced and activated; While ‘↓’ represents decreased, downregulated, inhibited

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