Background: Ductal carcinoma in situ (DCIS) recurs in the same breast follo
wing breast-conserving surgery in 5%-25% of patients, with the rate influen
ced by the presence or absence of involved surgical margins, tumor size and
nuclear grade, and whether or not radiation therapy was performed. A recur
rent lesion arising soon after excision of an initial DCIS may reflect resi
dual disease, whereas ill situ tumors arising after longer periods are some
times considered to be second independent events. The purpose of this study
was to determine the clonal relationship between initial DCIS lesions and
their recurrences. Methods: Comparative genomic hybridization (CGH) was use
d to compare chromosomal alterations in 18 initial DCIS lesions (presenting
in the absence of invasive disease) and in their subsequent ipsilateral DC
IS recurrences (detected from 16 months to 9.3 years later). Results: Of th
e 18 tumor pairs, 17 showed a high concordance in their chromosomal alterat
ions (median = 81%; range = 65%-100%), while one case showed no agreement b
etween the paired samples (having two and 20 alterations, respectively). Mo
rphologic characterization of the DCIS pairs showed clear similarities. The
mean number of CGH changes was greater in the recurrent tumors than in the
initial lesions (10.7 versus 8.8; P = .019), The most common changes in bo
th the initial and the recurrent in situ lesions were gains involving chrom
osome 17q and losses involving chromosomes 8p and 17p, The degree of concor
dance was independent of the time interval before recurrence and of the pre
sence of positive surgical margins. Conclusions: In this study, DCIS recurr
ences were clonally related to their primary lesions in most cases. This fi
nding is consistent with treatment paradigms requiring nide surgical margin
s and/or postoperative radiation therapy.