Initial Evaluation of Melanoma: Title and subTitle BreakDon't Stop Getting That Chest X-ray . . . Yet

IN THIS issue of the ARCHIVES, Terhune et al¹ present a straightforward and useful analysis of the findings of an initial staging chest x-ray film in their series of patients with melanoma. They report that the chest radiograph of only 1 of their 876 patients showed a true-positive chest x-ray film at the time of diagnosis, but that the radiographs of 130 others had false-positive studies, necessitating additional evaluation. They conclude in part that initial chest x-ray films "may be neither useful nor cost-effective" for patients with stage I or intermediate-thickness stage II melanomas. While this study shows that chest radiography is unlikely to uncover occult pulmonary metastases at the time of diagnosis, it does not dissuade me from continuing to obtain a baseline chest x-ray film for patients with invasive melanoma that is thicker than 0.75 mm.

Chest radiography at the time of diagnosis of invasive melanoma is widely recommended and widely practiced.^{2 ,4 - 7} As Terhune et al point out, this study is performed so frequently because "the lung is one of the most common visceral sites of spread and a chest radiograph is relatively inexpensive, low risk, widely available, and easy to perform."¹ An initial chest x-ray film has 2 functions: first, it attempts to establish whether metastatic disease is present at the time of diagnosis, and second it documents the baseline examination.^{4 - 6}

It is a well-established fact that 5-year survival of patients with melanoma decreases with increasing tumor thickness at the time of diagnosis. While patients with tumor thickness less than 0.75 mm have 5-year crude survival rates of about 96% to 99%, survival begins to drop off significantly for thicker tumors.⁷ According to Terhune et al, the 5-year survival rate of patients in their study with stages I and II disease is approximately 80%, indicating that perhaps "20% of patients . . . have occult distant metastases at the time of diagnosis."¹ Thus, statistically we might expect that about 175 of the 876 patients in this study would eventually manifest metastatic disease. Several of these patients would presumably present with lung metastases since, as the authors point out, the lungs are the most common visceral site of metastasis.^{8 - 9} In fact, Terhune et al report that of those patients in their study for whom long-term follow-up was available, 30 developed lung metastases. In how many of these cases did the baseline chest radiograph eventually prove to be helpful or even cost-effective by avoiding other diagnostic procedures or altering choices of therapy? When a lung nodule or mediastinal mass appears on a chest radiograph, one of the first diagnostic steps taken is to compare the film with previous studies to ascertain whether the lesion is new.¹⁰ Squire and Novelline¹¹ write in the Fundamentals of Radiology,

Any chest film is only a point on a curve in the course of the patient's disease. Change from film to film . . . often alters the whole spectrum of diagnostic possibilities considered on viewing the original film.

Furthermore, many clinicians perform not only an initial chest x-ray film but follow this up with annual chest radiographs (particularly for high-risk tumors).⁶ Should this practice be abandoned as well? If so, how would metastatic melanoma be detected? Is it acceptable to wait until patients present with symptoms and signs of metastases such as weight loss, dyspnea, or skin lesions?

Further arguing against taking chest x-ray films at the time of diagnosis, Terhune et al state that the 15% false-positive rate led to costly additional evaluation.¹ The authors report that additional investigations of suspicious x-ray film findings included comparison with previous chest x-ray films, a repeated chest x-ray film, or a chest computed tomographic scan. However, we are not told in how many cases each of these were required. Repeated chest radiographs or comparisons with previous x-ray films might not present a notable expense. A cost-benefit analysis would be useful here.

Melanoma is among the most deadly of all dermatologic diseases; taking a chest radiograph at the time of diagnosis is a routine component of care for patients with melanoma. It not only allows the physician to look for evidence of metastatic disease in the thorax but also provides a baseline examination that may prove to be of future value, particularly since the lungs are the most common site of visceral metastasis. Terhune et al have provided important perspective on the significance of the initial chest x-ray film—it is not likely to uncover metastatic disease at the time of diagnosis. However, their study does not prove that the initial chest radiograph is not cost-effective or not useful as a baseline examination.

The chest radiograph is widely available, relatively inexpensive, and noninvasive. No studies have been done that satisfactorily prove that it is not useful and not cost-effective. In the absence of such studies, our obligation to patients with a significant risk of manifesting metastatic disease, particularly those with an invasive melanoma thicker than 0.75 mm, is best met by continuing to obtain a baseline chest x-ray film at the time of diagnosis.