https://www.vetsurgeon.org/f/clinical-questions/9899/mammary-development-in-male-guinea-pigs I&#39;m posting this on behalf of a colleague so sorry if I miss any details She has a client with 2 male guinea pigs both of which have started with bilateral mammary development. They both have a serous discharge- one is slightly milky. Antibioticsen-USTelligent Community 10https://www.vetsurgeon.org/thread/49679?ContentTypeID=1Fri, 18 Nov 2011 12:20:45 GMT146601cc-3922-4be7-9974-7e1d4e45a66b:79f651b8-b341-4fa3-95c1-fd98158d5408Dagmar Steele<p>I would think of neoplasia too, even if &nbsp;there are two affected males, life is strange sometimes and I cannot think of anything infectious that would cause mammary lumps in guinea pigs. I have had good results with removal in the past.</p><div style="clear:both;"></div>https://www.vetsurgeon.org/thread/49677?ContentTypeID=1Fri, 18 Nov 2011 11:23:52 GMT146601cc-3922-4be7-9974-7e1d4e45a66b:7596dedc-adc0-44f6-adc6-5e5420c45910Mark Rowland<p>Hi there,</p> <p>top ddx mammary gland adenocarcinoma Im afraid. </p> <p>biopsy or fna if you like but surgical excision would be what I would be thinking about</p> <p>Goodluck</p><div style="clear:both;"></div>