SYMPOSIUM OF BREAST IMAGING EDITORIAL

Breast cancer is the most common neoplasm found among women in the Western world. Its early diagnosis is based the breast self-examination, physical breast examination performed by an experienced physician and mammography. Breast cancer diagnosis is usually confirmed by way of punction cytology in non-palpable lesions or by biopsy in palpable breast lesions. Mammography is the most useful diagnostic imaging method for screening and diagnosing breast cancer. However, and in spite of the technical improvements introduced in recent years, mammography still has some diagnostic limitations. Its sensitivity decreases in some circumstances, such as dense breast, breast prosthesis or following radiation, surgery or biopsy. Its false negative rate is between 10% and 15%. A false negative mammogram contributes to a delay in breast cancer diagnosis and results in poorer prognosis [1]. Moreover, mammography is frequently incapable of differentiating malignant lesions from benign ones. Finally, most published studies have obtained a positive predictive value for mammography that ranges between 10% and 40%, which results in a high number of breast biopsies being performed on benign lesions [1]. This leads to an increased financial cost and the possibility of making subsequent mammographic evaluation more difficult. Various diagnostic procedures have been used in an attempttoresolvesomeoftheselimitations.Thus,withinthe `anatomically based' diagnostic procedures, we can include ultrasound, colour Doppler ultrasound, digital mammography, computed tomography and magnetic resonance imaging. Single photon emission tracers have been used in the studyof breast cancer formore than 50 years, but the first reports using P, Tc diethylenetriaminepentaacetic acid (Tc-DTPA), Tc-pertechnetate or Ga were discouraging. The 1980s to 1990s saw the appearance of a new age of radiopharmaceuticals used in the study of breast cancer, with the use of Tl, Tc tetrofosmin, Tc methylene diphosphonate (Tc-MDP) and, fundamentally, Tc hexakis-2-methoxyisobutylisonitrile (Tc sestamibi or Tc-MIBI). Other radiopharmaceuticals, such as In octreotide or radiolabelled monoclonal antibodies, offer a new approach in the study of breast cancer. Today we can consider that Tc-MIBI is the single photon tracer of choice in the study of breast cancer, although, and despite of its broad clinical experience, its precise uptake mechanism into the tumour cells is not clearly understood. We know that more than 90% of the activity is located in the mitochondria. Experimental studies suggest that the main factor which appears to intervene in the uptake of the radiopharmaceutical is the electrostatic attraction between the positive charge of the Tc-MIBI and the negative charge of the mitochondria [2]. But Tc-MIBI uptake into the tumour cells is not a simple process; other factors that have been suggested in the radiopharmaceutical uptake are tumour perfusion, histological type, metabolic request or passive membrane diffusion. It is also important to point out the relationship between the cellular washout of Tc-MIBI and the cellular expression of the P-glycoprotein, associated with resistance to chemotherapy [3]. The main advantage of scintimammography in the study of breast cancer is that its functional basis makes this technique a useful complement to mammography, resolving some of its main limitations. In this context, we must recall that Tc-MIBI uptake is not related with breast tissue density or with the presence of scar tissue or prosthesis. Furthermore, Tc-MIBI can differentiate benign from malignant breast lesions and, thus, scintimammography can increase the low positive predictive value of the mammography [4]. We must always bear in mind that mammography and scintimammography are complementary techniques. We cannot understand the significance of the scintimammography without a previous knowledge of the mammography. The development of high resolution breast dedicated cameras, and radioguided stereotactic breast biopsy could be two of the most important future perspectives of scintimammography [5]. A further step in the development of nuclear medicine functional images in the study of breast cancer has been the introduction of positron emission tomography (PET). PET using F-fluorodeoxyglucose (F-FDG) is a wellestablished diagnostic method in oncology. Its use is based on the increase of glucose metabolism in malignant cells. Whole-body PET imaging has the advantage that