Environmental Factors. Environmental influences are suggested by the variable incidence of breast cancer in genetically homogeneous groups (e.g., Japanese women living in Japan and the United States) and the geographic differences in breast cancer incidence, as discussed earlier.
MORPHOLOGYThemostcommonlocationoftumorswithinthebreastisintheupperouterquadrant(50%),followedbythecentralportion(20%).About4%ofwomenwithbreastcancerhavebilateralprimarytumorsorsequentiallesionsinthesamebreast.
Breastcancersareclassifiedmorphologicallyaccordingtowhethertheyhavepenetratedthebasementmembrane.Thosethatremainwithinthisboundaryaretermedin situ carcinomas, andthosethathavespreadbeyonditaredesignatedinvasive carcinomas. Inthisclassification,themainformsofbreastcarcinomaareasfollows:
A.Noninvasive 1.
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B.Invasive 1.
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Therearetwomorphologictypesofnoninvasivebreastcarcinoma:ductalcarcinomainsitu(DCIS)andlobularcarcinomainsitu(LCIS).Thetermsductal andlobular aremisleading,asbothtypesofCISarethoughttoarisefromcellsintheterminalductthatgiverisetolobules.LCISusuallyexpandsinvolvedlobules(
Fig.19.28A ),whereasDCISdistortslobulesintoductlikespaces(
Fig.19.28B ).Bydefinition,both“respect”thebasementmembraneanddonotinvadeintostromaorlymphovascularchannels.
DCIShasawidevarietyofhistologicappearances,includingsolid,comedo,cribriform,papillary,micropapillary,and“clinging”types.Nuclearappearancesrangefromblandandmonotonous(lownucleargrade)topleomorphic(highnucleargrade).Thedistinctivecomedosubtypeischaracterizedbyextensivecentralnecrosis,whichproducestoothpastelikenecrotictissuethatextrudesfromtransectedductsonapplicationofgentlepressure.CalcificationsfrequentlyareassociatedwithDCIS(
Fig.19.28C ),resultingfromcalcificationofnecroticdebrisorsecretorymaterial.DCISconstitutesonly5%ofbreastcancersinunscreenedpopulationsbutupto30%inscreenedpopulations,largelybecauseoftheabilityofmammographytodetectcalcifications.CurrenttreatmentstrategiesforDCISusesurgeryandirradiationtoeradicatethelesion.Treatmentwithanti-estrogenicagentssuchastamoxifenalsoisusedtodecreasetheriskofrecurrenceofER-positiveDCIS.Theprognosisisexcellent,withgreaterthan97%long-termsurvival.Ifuntreated,DCISprogressestoinvasivecancerinroughlyone-thirdofcases,usuallyinthesamebreastandquadrantastheearlierDCIS.
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Fig.19.28Carcinomainsitu.(A)Lobularcarcinomainsitu(LCIS).(B)Ductalcarcinomainsitu(DCIS).DCISpartiallyinvolvesthelobuleinthelowerhalfofthisphotoandhascompletelyeffacedtheupperlobules,producingaductlikeappearance.(C)MammographicdetectionofcalcificationsassociatedwithDCIS.