Cluster of lymph nodes in cats breast?

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I recently noticed some lumps in my cats breast, shes a seven year old blue point siamese. I took her to the vet and they did some tests, a few weeks later they got back to me saying it was a cluster of benign lymph nodes. The vet said they had to send out the tests more than once cause they could not figure out what it was at first, as they had never seen this before. Has anyone ever had this happen to any of their pets? It worries me that my cat had, the mass has been removed, something that even the experts could not figure out what it was. Any help would me appreciated. Thank you.