This report describes the first case of a pregnant woman presenting low-back pain and breast pain associated with bilateral erythematous breast hypertrophy, proving to be the result of metastatic disease from a gastric carcinoma. A 30-year-old pregnant woman was admitted complaining of persistent severe low back pain, breast pain and concomitant bilateral erythematous breast hypertrophy, mimicking primary inflammatory breast carcinoma. During the caesarean section, widespread disease was found and finally metastatic gastric cancer was detected. Pregnant women with gastric cancer may present symptoms that are considered common during pregnancy. Common symptoms that present warning characteristics, such as the persistent severe pain observed in the presented case, should be carefully investigated as they may be the only warning signs and symptoms of rare ominous conditions such as gastric cancer.