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Why does my dog have a new mammary lump and swelling post-surgery?

Updated On September 23rd, 2025

Pet's info: Dog | Shih Tzu | Female | spayed | 10 years and 8 months old | 12 lbs

My 10 year old dog had a lump in her 4th left mammary gland, so we had it removed. The test came back inconclusive, so we don't know if it was malignant or not. Her vet recommended having her sprayed as well, so she had two procedures done. It has been a month since her surgery and now there appears to be a quarter size lump near her 4th right mammary gland. Also, near her vulva, where her stitiches were, looks a little swollen.

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2 Answers

Most Helpful Answer

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Answered By Lauren Barry, BVSc, MRCVS, DVM

Veterinarian

Published on October 30th, 2017

I would be concerned that the swelling is another mammary mass or lymph node from the mammary area. Unfortunately, needle aspirates on mammary cells can be hard to determine if malignant or not. I would recommend taking Aries in to your vet tomorrow to discuss the next steps. I think your vet will also suggest chest xrays to make sure there is no evidence of cancer in her lungs.

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    Answered By Ricardo Fernandez, DVM

    Veterinarian, Veterinary Oncology Resident

    Published on

    Thanks for using Petco Pet Education Center, formerly Petcoach! Mammary tumors in dogs are malignant in about 50% of cases which makes it possible that her previously removed tumor was malignant in nature. I recommend that you check with your veterinarian for further staging (to check for any evidence of metastasis or spreading) which should include thoracic radiographs and abdominal ultrasound as well as sampling of this lesion. If no evidence of metastasis is noted and it does appear to be a tumor, a lumpectomy is recommended. If confirmed an adenocarcinoma, chemotherapy is generally recommended. Feel free to request a consultation with me if you would like to obtain further information as this is a type of issue I deal with very commonly and could give you more information after gathering more information from you about her case. Good luck and have a good night!

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