Comparison of the relative expression of estrogen receptor (ER)variant truncated after sequences encoding exon 2 of the wild-type (WT)ER-α (ERC4) messenger RNAs between breast tumor and adjacent matchednormal breast samples. (A) Total RNA extracted from frozen tissuesections from tumor (T) and adjacent normal (N) breast tissue samples wasreverse transcribed and polymerase chain reaction (PCR) was amplified usingERU, ERL and C4L primers (see text). Radioactive PCR products were separated ona 6% acrylamide gel and visualized by autoradiography. Bands migrating at 149and 536 base pairs were identified as corresponding to WT-ER and ERC4 variantmessenger RNA, respectively. C, negative control (no complementary DNA addedduring the PCR reaction). (B) For each case, signals corresponding toERC4 variant messenger RNA were quantified (see text) and expressed inarbitrary units for tumor (black column) and normal (white column) components.For each sample, the mean and the standard deviation of at least threedifferent PCR assays are indicated. Cases are sorted by ER status (black bottomlane) and progesterone receptor (PR) status (gray bottom lane). Thesignificance of the differences between tumor and normal matched componentswithin each subgroup, as tested using the Wilcoxon matched-pair test, isindicated where P <0.05. M, molecular weight marker (fx174 Haellldigest, Gibco BRL, Grand Island, New York, NY).