The present invention is directed to novel non-invasive diagnostic tools/compounds to image and treat cancers, especially cancers which overexpress GnRH such as breast cancer, prostate cancer and melanoma, among others, including metastatic breast cancer, prostate cancer and/or melanoma among numerous others in vivo. The novel imaging probes are capable of detecting cancerous cells, as well as their metastatic spread in tissues. The novel probes of the present invention will also be useful to initiate therapy for breast and/or prostate cancer, among other cancers, as well as monitor patients' response to chemotherapy treatments and other interventions or therapies used in the treatment of cancer, including metastatic cancer as otherwise described herein. Compounds according to the present invention may be used as diagnostic tools for diagnosing cancer as well as therapeutic agents for treating cancer and related secondary disease states and conditions.