Lumps in the groin are generally secondary to lymph node growth and may have benign or malignant characteristics. Benign growths are usually secondary to inflammation or infection, they grow in a couple of days and usually (but not always) hurt when you press them. Malignant lymph node growth usually does not cause pain unless they get too big, are hard and fixed to the sorrounding structures. Because of your history of breast cancer it is important to have it checked right away. Many factors have to be considered: If you have been cancer free, how long has its been since your breast cancer was treated. CA marker for breast cancer, though it can be a tool to monitor disease activity (when present) it dose not have the sufficient specificity or sensitivity to detect cancer recurrence. (it may elevate without cancer being back and cancer may return without elevation of CA marker).