The National Cancer Institute created originally the Common Toxicity Criteria (CTC) to aid in the recognition and grading severity of adverse effects caused by chemotherapy treatments.

NCI-CTCAE Grading Scale* 

Grade	Description
Grade 0 (none)	None
Grade 1 (mild)	Painless ulcers, erythema, or mild soreness in the absence of lesions
Grade 2 (moderate)	Painful erythema, oedema, or ulcers but eating or swallowing possible
Grade 3 (severe)	Painful erythema, oedema, or ulcers requiring IV hydration
Grade 4 (life-threatening)	Severe ulceration or requiring parenteral or enteral nutritional support or prophylactic intubation
Grade 5 (death)	Death related to toxicity

* Specific NCI-CTC grading scales related to radiation and bone marrow transplantation have been formulated and are described in Sonis et al. 2004.

Reference:
NCI-CTC v 2.0, 1999 : http://ctep.cancer.gov/
Sonis et al. Cancer 2004; 100(9 Suppl):1995-2025.