Molecular subtypes of breast cancers detected in mammography screening and outside of screening.
OBJECTIVE
The frequency and significance of gene expression profile-derived molecular subtypes of breast cancers found in mammography screening are unknown.


METHODS
We identified breast cancers diagnosed in women of any age living in defined geographic regions in Finland in 1991 to 1992 and collected clinical and pathologic data. Surrogates for the molecular subtypes were determined for 247 cancers found in organized mammography screening and 989 cancers detected outside of screening using immunohistochemistry or in situ hybridization. Molecular subtypes were defined as luminal A [estrogen receptor (ER) positive and/or progesterone receptor (PR) positive, HER2-], luminal B (ER+ and/or PR+, HER2+), basal-like (ER-, PR-, HER2-, cytokeratin 5+, and/or HER1+), HER2+/ER- (ER-, PR-, and HER2+), and unclassified. The median follow-up time was 9.4 years.


RESULTS
The luminal type A was common (73.7%) and the HER2+/ER- type is rare (5.7%) in screen-detected cancer, and only 16% were HER2 positive. Women with cancer diagnosed in screening at ages 50 to 69 years had similar molecular subtype distribution as women whose cancer was found outside of screening at age >69 years. In a multivariate model, cancer detection at screening independently predicted favorable distant disease-free survival when the molecular subtype was included as a covariate in addition to age, histologic grade, and cancer size. Women with small (pT(1)N(0)M(0)) HER2-positive cancer had similar outcome regardless of the method of detection.


CONCLUSIONS
Molecular subtype distribution of screen-detected breast cancer differs from that of cancers found outside of screening and accounts in part for the better outcome of screen-detected cancer.
Sihto
Harri
H
Laboratory of Molecular Oncology, Biomedicum, Helsinki University Central Hospital, Helsinki, Finland.
Lundin
Johan
J
Lehtimäki
Tiina
T
Sarlomo-Rikala
Maarit
M
Bützow
Ralf
R
Holli
Kaija
K
Sailas
Liisa
L
Kataja
Vesa
V
Lundin
Mikael
M
Turpeenniemi-Hujanen
Taina
T
Isola
Jorma
J
Heikkilä
Päivi
P
Joensuu
Heikki
H
D000328:Adult; D000368:Aged; D001943:Breast Neoplasms / Q000175:diagnosis* / Q000473:pathology*; D018572:Disease-Free Survival; D005260:Female; D005387:Finland; D006801:Humans; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D008327:Mammography / Q000379:methods*; D008403:Mass Screening / Q000379:methods*; D008875:Middle Aged; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000096:biosynthesis / Q000235:genetics*; D012042:Registries; D013997:Time Factors
D018719:Erb-b2 Receptor Tyrosine Kinases