The aim of this study is to demonstrate the significance and necessity of radionuclide diagnostics of oncologic pathology of different nature on the instance of a clinical case of detection of multiple foci of secondary nature (mts) of parathyroid gland tumor by skeletal bone scintigraphy in the course of routine examination of a patient for breast cancer. The data from the medical records, protocols and radiation methods of examination of the patient were used as the study material. During a routine examination for metastases of breast cancer through radionuclide examination of the parathyroid glands and scintigraphic examination of the skeletal bones, pathologic foci of radiopharmaceutical (RP) hyperfixation were detected in the patient. On further computed tomography (CT) of the knee joints it was found that the picture may correspond to multiple secondary lesions of the skeletal bones on the background of parathyroid gland disease. After a week the patient underwent a biphasic radionuclide study of the parathyroid glands, which made it possible to assess the presence of obvious scintigraphic signs of hyperfunctioning adenoma of the left lower parathyroid gland. Further, a thyroid gland (TG) tissue biopsy study was performed, which showed that the tissue fragment on the section was light brown with the presence of a cyst filled with brown fluid, which may correspond to a brown tumor. Thus, a patient with main breast disease is likely to be diagnosed with other unrelated cancers. The key diagnostic method in this case will be a scintigraphic study with single photon emission computed tomography (SPECT), which provides the most accurate visualization of pathology, its description and prediction of further therapy both in outpatient and inpatient settings. For the majority of cancer patients it is advisable to conduct regular examination with the help of scintigraphy for the purpose of prevention and early detection of concomitant pathology.