Fig. 19.23B ). As with symptomatic breast lesions, the likelihood that an abnormal mammographic finding is caused by malignancy increases with age, from 10% at age 40 to more than 25% in women older than age 50.
Symptomsaffectingthebreastsareevaluatedprimarilytodetermineifmalignancyispresent.
Regardlessofthesymptom,theunderlyingcauseisbenigninthemajorityofcases.
Breastcancerismostcommonlydetectedbypalpationofamassinyoungerwomenandinunscreenedpopulationsandbymammographicscreeninginolderwomen.
Inflammatory diseases of the breast are rare and may be caused by infections, autoimmune disease, or foreign body–type reactions. Symptoms include erythema and edema, often accompanied by pain and focal tenderness. Because inflammatory diseases are rare, the possibility that the symptoms are caused by inflammatory carcinoma should always be considered (discussed later).
The only infectious agent to cause breast disease with any frequency is Staphylococcus aureus, which typically gains entry via fissures in nipple skin during the first weeks of breastfeeding. The invading organisms may lead to the formation of “lactational abscesses,” collections of neutrophils and associated bacteria in fibroadipose tissue. If untreated, tissue necrosis may lead to the appearance of fistula tracks opening onto the skin. Most cases are treated adequately with antibiotics and continued expression of milk. Rarely, surgical incision and drainage is required.
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The two types of stroma in the breast, intralobular and interlobular, give rise to different types of neoplasms (
Fig.
19.22 ). Historically, tumors derived from intralobular stroma have been cleanly divided into benign fibroadenomas and more cellular phyllodes tumors, which sometimes recur following excision and rarely pursue a malignant course. It is now appreciated that these tumors share driver mutations in the same genes and appear to be part of a spectrum of related neoplasms. Nevertheless, the old classification is engrained in the medical lexicon and we will follow it here for simplicity’s sake.
MORPHOLOGYTumorsderivedfromintralobularstromaarecomprisedofbothstromalcellsandepithelialcells(i.e.,theyare“biphasic”),astheneoplasticproliferationofspecializedlobularfibroblastsalsostimulatesreactiveproliferationoflobularepithelialcells.Astheintralobularfibroblastsproliferate,theypushanddistorttheepithelialcellssothattheyformelongatedslitlikestructuresratherthanroundacini.Inbenignfibroadenoma,thetumormasshascircumscribedbordersandlowcellularity(
Fig.19.24A);mitoses arerare.Bycontrast,inphyllodestumorsthestromalcellstendtooutgrowtheepithelialcells,resultinginbulbousnodulesofproliferatingstromalcellsthatarecoveredbyepithelium(
Fig.19.24B ),thecharacteristic“phyllodes”(Greekfor“leaflike”)growthpattern.Inhigh-gradephyllodestumorsepitheliummaybescantorabsent,producingasarcomatousappearance.Overall,about2%ofphyllodestumorsmetastasizetodistantsites.