用细胞做mtt assay, proliferation assay, apoptosis assay等等, 我可以称之为 study at the cellular level, 检测肿瘤样品的某些基因的mRNA, protein level, 我 可以称之为study at the molecular level, 那如果观察老鼠的tumor incidence, tumor latency, tumor growth, metastasis rate, 该怎么说,a study at xxx level ?