To avoid false negatives in a screening program to detect breast cancer among women over 50 years of age, the test must be:

Breast cancer develops as a result of the uncontrolled growth of abnormal breast cells. While healthy breast cells are able to continually renew themselves in an orderly fashion, abnormal cells may divide haphazardly, without control or order. The extra cells created can form malignant, or cancerous, tumors which, if left untreated, can spread to other parts of the body. There are many different types of breast cancer. The most common are invasive ductal cancer, which begins in the duct cells, and invasive lobular cancer, which begins in a lobule, where milk-producing glands are present. A patient facing a breast cancer concern likely has many questions. Choosing the right cancer center for consultation, diagnosis and support is the most important step toward achieving lasting, positive results.  
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For more information, check out:
https://moffitt.org/cancers/breast-cancer/

Sodium is the answer