4) p21- tumor response to larger fraction-size: This response is observed in five cell lines and is characterized at the cellular level by diminished expression of p21 (DLD-1, 19S186, 80S4, SW1222 and U251) and at the tumor level by common enhanced sensitivity only to large fractions (15 Gy). The gene discussed is CDKN1A; the disease is neoplasm.