For "kind, gentle, harmless":
* Kind
* Gentle
* Mild
* Harmless
* Innocuous
* Non-malignant
* Non-threatening
For "favorable, not dangerous":
* Favorable
* Positive
* Beneficial
* Salutary
* Auspicious
* Prosperous
For "not cancerous":
* Non-cancerous
* Non-malignant
* Non-invasive
Please provide the context of the word "benign" in your sentence, and I can give you a more accurate synonym.