Carcinocinum or all other homeopathic remedies are absolutely safe to take in homeopathic doses if agrees with the symptoms of patient and potency / dose is selected by a certified classical homeopathic Doctor.
These are available in many potencies. Homeopathic medicines are prescribed on the basis of symptom similarity. Carcinosinum is often more commonly indicated in cases where there is some family history of cancer. But that is not an only factor.