In a previous work, we have isolated the human H19 gene and shown accumulation 
of transcripts in various human tumors including breast carcinomas (Douc-Rasy et 
al (1993) Int J Oncol 2, 753-758). Questions arose, after Northern blot results, 
about the precise H19 mRNA location, specially in normal breast tissues and 
benign or malign primary breast tumors. Then we performed molecular in situ 
hybridization to get insight into tissue expression of the H19 gene. Examined 
resections included one normal tissue, one fibroadenoma and 13 cancers. Results 
obtained with the H19 probe can be summarized as follows: 1) in normal breast 
tissues signals were focally observed in epithelial cells, but more 
predominantly in the palleal tissue which is sensitive to hormones; 2) in the 
fibroadenoma, fibroblastic cells were extensively labeled at the 
stroma-epithelium boundary, but epithelial cells were negative; and 3) in 
primary cancers, eight specimens exhibited signals on stromal cells, one 
specimen on epithelial cells and four on both epithelial and stromal cells. Data 
provide the following evidence: 1) usually labeled cells are clustered, either 
within normal or pathological tissues; 2) the labeling pattern highly differs 
from one tumor to another; and 3) H19 probe displays very different signals from 
one cell to another in given compartment of a given tissue section. In 
conclusion, it seems that a high H19 expression matches the tumor invasion. Our 
results suggest that the expression of this gene is concerned by the 
relationships between epithelial and stromal cells, and can reflect peculiar 
physiological states of the cells. Furthermore, we discuss results showing an 
abundant expression of H19 gene in some adenocarcinomas of bad prognosis, in the 
context of the otherwise established tumor-suppressor role of this gene, or the 
strictly controlled gene dosage, which could be overridden in these particular 
cases.