Observation, or watchful waiting, is most appropriate for this elderly man with newly diagnosed prostate cancer and medical comorbidities after the benefits and risks of this approach are discussed with the patient. Observation is based on an assessment that a patient would not benefit from definitive treatment of prostate cancer, either because of significant comorbidities or a shortened life expectancy, with the expectation that palliative treatment could be provided if the disease progresses. This patient's prostate-specific antigen (PSA) level, extent of disease based on biopsy findings, and Gleason score are all predictors of low-risk disease. Furthermore, he has a significant medical history, including worsening heart failure. Given that this patient has very low-risk prostate cancer and a life expectancy most likely less than 10 years, observation is the most appropriate management option for this patient.

Active surveillance, in contrast to observation, is the postponement of definitive therapy with the intent to pursue treatment of curative intent if there is evidence of disease progression. Active surveillance involves a program of regular assessment with physical examination, PSA testing, and prostate biopsy. It would not be appropriate for this patient, given his life expectancy related to significant medical comorbidities.

Cryotherapy is a technique that freezes prostatic cancer cells to treat localized prostate cancer. However, its role as a treatment option for localized prostate cancer has not been established at present.

Both external-beam radiation therapy and radical prostatectomy are reasonable alternatives for definitive treatment in patients considered appropriate candidates for therapy. However, the risks of either would likely outweigh the benefits of treatment in this patient with low-risk disease and significant medical comorbidities.