Korelasi kadar osteopontin terhadap pengecilan tumor pada kemoradiasi neoajuvan kanker rektum stadium lanjut lokal dievaluasi dengan pemeriksaan radiologi dan enzyme-linked immunosorbent assay = Osteopontin level correlation with tumor shrinkage in neoadjuvant chemoradiation of locally advanced rectal cancer using radiology evaluation and enzyme-linked immunosorbent assay