The value of MRI in showing occult breast cancer Occult breast cancer (OBC) refers to breast cancer without breast lumps but with metastatic cancer as the clinical manifestation, which is a rare type of breast cancer with special clinical manifestation. OBC is a rare type of breast cancer with a special clinical presentation, but the small size of the primary tumor and the large size of the metastatic tumor may be due to their differential growth. As for the reasons of occult primary carcinoma in breast, some scholars analyzed 25 cases of OBC and concluded that: (1) the primary tumor is small; (2) the whole breast tissue is thickened due to fibrous mastitis which hinders the detection of small primary foci; (3) the location of the foci is deeper and most of them are pimple-like carcinoma which is not conducive to the detection. We have found two cases of OBC with axillary mass as the first symptom, but no breast mass was detected by clinical examination, x-ray mammography and ultrasound, and the ipsilateral breast primary foci were detected by MRI. In one case, the MR scan T2W1 showed a diffuse signal increase in the affected breast, and no mass was found. The dynamic enhancement subtraction image showed a small nodule with an early (within 1 min) significant enhancement of about 6 mm in diameter in the outer upper quadrant of the breast, and the MIP (maximum intensity projection) showed multiple thickened and distorted vascular shadows around the lesion. The MR diagnosis was breast cancer, followed by radical mastectomy, and the disease was examined as intraductal carcinoma. In another case, the MR scan did not reveal any significant abnormality, but the dynamic enhancement subtraction showed a significantly enhanced lobulated nodule in the deep part of the breast, with a diameter of about 9 mm and a type II signal intensity and time curve, and the surgical pathology confirmed that it was an invasive ductal carcinoma. This led to the conclusion that enhanced MRI has a high sensitivity for OBC that is negative on clinical and x-ray examination. 2. The value of MRI to show multifocal and multicentric breast cancer Multifocal and multicentric growth are the two more common biological characteristics of breast cancer. Multifocality refers to the presence of microscopic foci of varying scope and number around the main cancer; while multicentricity refers to the presence of microscopic foci far away from the main cancer and located in other quadrants of the breast, i.e. not in the same quadrant as the main cancer. In this group, MRI showed four cases of multifocal breast cancer in 17 cases, which were manifested as one large mass surrounded by small foci of varying size. In 6 cases, MRI showed multicentric breast cancer, showing multiple nodes or masses in different quadrants of the breast, including one case with as many as 5 lesions. The results revealed 3O cases of multifocal breast cancer, 24 cases of multicentric breast cancer and 15 cases of bilateral breast cancer that could not be detected by conventional examination, thus showing that the advantages of MRI in showing multifocal and multicentric breast cancer cannot be underestimated, which is important for the formulation of treatment plans. 3. MRI assessment of pectoral muscle infiltration is very important for clinical staging and treatment planning of breast cancer. Elizabeth et al. performed dynamic enhancement MRI on 19 patients with deep breast cancer foci and found that 5 patients had pectoral muscle infiltration, which showed the destruction of posterior breast fat gap, discontinuity and abnormal enhancement of pectoral muscle, and emphasized that abnormal enhancement of pectoral muscle was an important sign of tumor invasion. The abnormal strengthening of the pectoral muscle was emphasized as an important sign of tumor invasion of the pectoral muscle. Six of the 19 cases showed pectoral muscle enhancement after enhancement, thus radical breast cancer resection of the pectoral muscle was performed and pectoral muscle invasion was confirmed by surgery, while preoperative mammography in these six patients did not indicate pectoral muscle infiltration. This shows that MRI is superior to x-ray in assessing the invasion of the pectoral muscle and chest wall by deep breast cancer. The axillary lymph nodes are the main route of lymphatic metastasis of breast cancer, and whether they are involved or not is important for the staging of breast cancer, prognosis and whether patients receive further adjuvant treatment. One study suggested that MRI of 17 breast cancer patients revealed enlarged and fused axillary lymph nodes in 11 cases, 9 cases (81.8%) were pathologically confirmed to have metastasis, and 2 cases were lymph node reactive hyperplasia; in the other 6 cases, no enlarged lymph nodes were found on MRI, but pathology confirmed lymph node metastasis in 2 of them. Therefore, I believe that MRI can assess axillary lymph node metastasis to a large extent, and only a few patients have false negative and false positive results. David et al. applied MRS to assess axillary lymph node metastasis in breast cancer patients and pointed out that the choline level in axillary lymph nodes with metastasis was significantly elevated, which has a high sensitivity and specificity, thus providing a new and more sensitive means of examining axillary lymph node metastasis in breast cancer. This provides a new and more sensitive screening tool for axillary lymph node metastasis in breast cancer. Therefore, MRI and MRS (magnetic resonance spectroscopy) have potential clinical applications as noninvasive tests for the assessment of axillary lymph node metastasis. In conclusion, breast MRI can help to detect occult breast cancer and multifocal and multicentric breast cancer, and help to assess the infiltration of deep breast cancer foci into the pectoral muscle and the metastasis of axillary lymph nodes, which is helpful for the correct clinical staging and treatment planning of breast cancer. For patients who have difficulty in diagnosing breast cancer by clinical diagnosis or conventional examination, and for those who are going to undergo breast-conserving surgery, breast MRI, especially dynamic enhanced MRI, is recommended.