Malignant conditions of the breast on MRI Scans
Ductal carcinoma in situ (DCIS)
DCIS is a biologically diverse disease. It may be low grade, intermediate grade, or high-grade. The most common morphologic feature of DCIS on MRI is nonmass enhancement (NME). NME is described in the ACR BI-RADS lexicon as enhancement that is not a mass but is still distinct from the surrounding normal breast tissue.
DCIS mostly presents as NME. Segmental and ductal patterns of enhancement are more suspicious than regional and diffuse enhancement. Clumped NME is the most common type of NME seen with DCIS. Clustered ringlike enhancement has been described as a type of NME that is strongly suspicious for DCIS. In a smaller number of cases, DCIS may be seen on MRI as a mass with irregular margins.
DCIS frequently shows slower initial and plateau or persistent delayed-phase enhancement. It is well known that DCIS may not show kinetic features that are regarded as typical for malignancy.
The variability of enhancement of DCIS is due to variations in neoangiogenesis, which in turn is somewhat related to the histologic grade.  Between 15 and 40% of DCIS cases show minimal to moderate enhancement that is indistinguishable from that of normal glandular tissues. This pattern tends to occur in low-grade DCIS, but it has also been described in comedocarcinoma.  DCIS of a high nuclear grade tends to have stronger enhancement than that of a lower-grade DCIS. Note that 40% of DCIS cases are not calcified, even when they are high grade  .
Paradoxically, although breast MRI is unsuitable for an evaluation of microcalcifications, it sometimes shows the extent of DCIS (calcified or noncalcified) better than mammography. Because this information has the potential to change the type and extent of surgical excision, breast MRI can prove useful for the local staging of DCIS, particularly when the noncalcified component is significant.
Invasive ductal carcinoma
On breast MRI, invasive ductal carcinoma (IDC) most often appears as an irregular, spiculated, or multilobulated mass with strong, rapid contrast enhancement that is at least 60% above baseline. Rim or inhomogeneous, centripetal enhancement on dynamic scans may be present. Typically, either a type II or type III enhancement curve is observed. Surrounding architectural distortion may be noted. About 5% of IDCs enhance slowly and/or less strongly, particularly if they are highly scirrhous.
Surrounding enhancement of variable intensity may represent DCIS; florid dysplasia; or benign, parenchymal enhancement. Breast MRI may show multifocal lesions or nipple/chest-wall involvement, which may not be otherwise evident. Multifocal IDC may show moderate, segmental, ductal enhancement connecting the masses; such masses are thus seen to be part of the same breast segment, even if they are not close to one another. Internal, enhancing septa are sometimes seen in invasive carcinomas; these should be distinguished from nonenhancing septations, which are typical in fibroadenomas.
Invasive lobular carcinoma
Invasive lobular carcinoma (ILC) accounts for 10-15% of breast carcinomas. ILC lesions can be mammographically occult or subtle in 20-40% of cases. [65, 66] As many as 85% are isointense relative to glandular parenchyma, and a minority have malignant microcalcifications.  The incidence of multifocal, multicentric, and bilateral, synchronous or metachronous involvement is much higher with ILC than with IDC.
Mammography and ultrasonography tend to underestimate the extent of ILC. Breast MRI has been shown to be more accurate, correctly demonstrating the extent of disease in about 85% of cases.  In the authors’ center, breast MRI is routinely used in all women with a preoperative diagnosis of ILC.
In most cases, ILC shows focal, irregular, strong, rapid enhancement typical of a malignancy. Single or multiple masses in one or more quadrants may be demonstrated. However, ILC occasionally has weak or moderate enhancement, and it may be difficult to distinguish from glandular parenchyma with this criterion alone. Recognizing this problem is easier if the diagnosis is already known from needle biopsy results. In these cases, a masslike contour or associated architectural distortion is usually present. Despite this limitation, breast MRI is better than conventional imaging for preoperative staging of breast ILCs.
Other breast malignancies
Mucinous or colloid carcinoma may be well defined, with a lobulated border and homogeneous enhancement. Superficially, these tumors may resemble a large fibroadenoma. However, these lesions are typically round rather than oval. Enhancing internal septa may be visible; if present, malignancy can be correctly diagnosed.  In rare cases, if an excess of mucin is present with relatively little malignant tissue, enhancement may be unremarkable or even absent.
Papillary and tubular carcinomas may enhance strongly and rapidly. However, some of these tumors have weak angiogenesis, which reflects their relatively low biologic aggression. These lesions may then enhance relatively slowly and/or weakly. 
Non-Hodgkin lymphoma of the breast is rare and usually secondary to involvement elsewhere in the body. Primary lymphoma may be synchronously or metachronously bilateral; in some cases, it grows rapidly and forms a large mass. These tumors can be occasionally confused with an invasive carcinoma, particularly if only needle-biopsy specimens are examined. Breast MRI can help in determining the intramammary extent of disease and may be useful for monitoring the response to chemotherapy.
In the breast, sarcomas are rare. Metaplastic carcinomas are also rare, but they may undergo sarcomatous transformation, most typically to osteosarcoma. These generally appear as a nonspecific mass with enhancement. Sometimes, they are remarkably rounded with circumscribed margins. However, they may have markedly heterogeneous enhancement secondary to tumor necrosis.
Phyllodes tumors are usually diagnosed with mammography, ultrasonography, and needle biopsy. Breast MRI adds little other than a true size measurement of large lesions. These lesions appear as large, circumscribed masses with rapid, strong enhancement; they often have internal lobulation and cystic spaces. [