Table 1.

Expression of the receptor tyrosine kinases Axl and Mer and the ligands Gas6 and Protein S in solid tumors.

Tumor Origin	Oncogene(s)	References
Bone	•	[125]
Brain	•••	[32, 55, 56]a
Breast	•••	[22, 33, 72–74, 76–78]b, c, d
Colon & rectum	•	[40, 126]
Endometrium	••	[127]
Esophagus	•	[128]
Gastrointestinal tract	•	[86]e
Kidney	••	[129, 130]f
Liver	•	[131]
Lung	••••	[23, 66–68]b
Mantle cell lymphoma	•	[132]
Ovary	••	[106, 133]
Pancreas	•	[24]b
Pituitary	•	[134]
Prostate	••	[28, 37, 123, 135]
Skeletal muscle	•	[136]
Skin	••	[137–139]
Stomach	•••	[25, 29, 140]g, h
Thyroid	••	[141–143]

^•indicates upregulation of Axl; • indicates upregulation of Mer; • indicates upregulation of Gas6; and • indicates upregulation of Protein S.

^aCoexpression of Axl and Gas6 correlates with poor prognosis.

^bOverexpression of Axlcorrelates with metastatic cancer and poor prognosis.

^cOverexpression of Axl is a mechanism of lapatinib resistance in vitro.

^dAxl expression correlates with ER expression; Gas6 expression correlates with ER and PR activation.

^eExpression of Axl is associated with imatinib resistance.

^fSerum Gas6 levels negatively predict survival.

^gCoexpression of Axl and Mer correlates with poor prognosis.

Overexpression of Gas6 correlates with lymph node metastasis.