I think there is a misunderstanding here unless you're referring to some different usage?

A node 'taking dye' indicates that it is a node where the cancer cells would most likely infiltrate the lymphatic system because the dye is injected in the vicinity of the tumor tissue to identify the lymph nodes most likely at risk. (Usually the nodes closest to the cancer cells but not always. Thus the dye is used to detect the pipeline.)

If the biopsy is negative, there were no cancer cells in that 'sentinel node.' That's good news.

The Oncotype service reps are very helpful. You might want to talk to them to find out the test algorithm dealing with lobular cancers. They have strict protocols for tissue submission so I would be surprised if the test is invalid. And they do reject tissue from tumors submitted for tests that are inapplicable for that particular tumor type or stage, etc. Or with a seemingly incorrect biopsy so are careful about the integrity of the tests' statistical universe appropriateness.