Response

I thank Dr DiTommaso for his letter and for the opportunity to further explain the relevance of the positive predictive values (PPVs) presented in Table 1.¹

I would absolutely endorse that physicians continue to investigate red flag symptoms. A workup of a patient with softer “low risk, but not no risk” symptoms is difficult for a physician. How does a physician identify the one patient who has cancer among the many who do not, all while preserving the patient-physician relationship when it is needed most? This is especially true given that many patients who develop cancer never display a clear high-risk symptom.

The PPVs were presented in part to show that studies have validated these “softer” symptoms. Hamilton et al clearly show that although individual symptoms might not strongly predict a cancer diagnosis, what is most important is the presence of multiple symptoms or non-resolving symptoms with multiple presentations, which together can result in a PPV risk of up to 20 times normal of developing a cancer.²

To appreciate why a symptom such as dyspnea has a PPV of only 0.66, it must be understood that dyspnea might be a symptom of other, more frequent non-malignant causes such as congestive heart failure or chronic obstructive pulmonary disease. If a patient presents multiple times with dyspnea, the PPV for lung cancer rises to 0.80, and continues to increase as it is combined with other symptoms: dyspnea and hemoptysis, PPV of 4.90; dyspnea and weight loss, PPV of 2.00; and dyspnea and loss of appetite, PPV of 2.00 (please see Figure 2 in Hamilton et al for more information).²

Unfortunately, there is no table that can definitively tell you which of your patients to work up for cancer and who to merely reassure. However, there is a recent study that shows that the PPV of a physician’s gut feeling for the diagnosis of cancer is 9.80.³ Perhaps your gut, and a combination of experience, clinical, and contextual knowledge, continues to be the best way to “draw the line.”

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