In preclinical tests in mice, a team at CSHL was able to dramatically change the character of an aggressive, metastatic primary breast tumor by targeting a single long non-coding RNA called Malat1 with a candidate drug called an antisense oligonucleotide (ASO). This image: Section of what doctors call an undifferentiated breast tumor -- densely packed with cancerous cells and with a high potential to spread. Next image: When treated with an antisense drug that specifically targets and reduces levels of Malat1, such tumors in mice were observed to undergo a change of character. The tumor becomes differentiated, its cells now cyst-like and filled with fluid that contains, among other things, milk proteins. The treated tumors were comparatively static, their metastatic activity reduced some 70 percent, the team reports.