Ann Thorac Surg 2006;81:1197-1198
© 2006 The Society of Thoracic Surgeons
Original article: General thoracic
Invited commentary
John A. Odell, MB ChB, FRCS(Ed)
Department of Surgery, Mayo College of Medicine, Mayo Clinic Jacksonville, 4500 San Pablo Rd, Jacksonville, FL 32224
The increased use of helical computerized tomographic (CT) scanning has resulted in the recognition of a radiographic opacity, termed ground-glass opacity (GGO). As the name suggests, the opacity is seen on CT scanning of the lung windows as a uniform grey opacity with vessels and bronchi traversing the opaque area, similar to a human form seen behind a shower door. The abnormality can be associated with inflammatory conditions, but it is usually due to bronchoalveolar carcinoma (BAC), a tumor with a propensity to affect woman more than men, to be multicentric, and to be without a strong smoking association. It also seems to have a more favorable prognosis even allowing for more advanced stage [1]. In animals, a lung tumor with indistinguishable histology to BAC is recognized, which is associated with the Jaagsiekte virus and transmittable, causing the same histologic features in the recipient, but viruses have never been found in human BACs [2].
Much of our knowledge of this condition comes from the Japanese literature in which CT scanning is used frequently as a screening examination. Noguchi and colleagues [3] classified adenocarcinomas into 6 subtypes A to F, increasing in malignant appearance and behavior. Types A, B, and C represent variants of BAC. Noguchi and colleagues [3] demonstrated that Types A and B are not associated with nodal metastases and have a very favorable prognosis if resected. Type C seems to be an advanced stage of types A and B. The BAC is one of the few tumors in which radiographic features frequently correlate with pathologic findings. It is recognized that if a solid component of the ground-glass opacity exists, then a more aggressive adenocarcinoma frequently exists. The Japanese resect these small ground glass opacities, usually as a wedge excision and often with video-assisted techniques. The lesions are difficult to feel within the lung when small so that localization techniques must, in their experience, be effectively used.
The Japanese literature also, in respect to this tumor, do not follow the TNM classification of tumors used elsewhere in the world; much of their literature concerns tumors classified as being less than 2 cm, whereas the T1 stage of the TNM classification refers to tumors less than 3 cm. This makes it difficult to compare series worldwide. It seems, however, that the Japanese have learned that GGOs greater than 2 cm demand more respect in terms of malignancy. The West has much to learn from the East with respect to this variant of tumor, and perhaps it is time to revise the TNM system or to classify these tumors differently. The presence of solid radiographic components on larger opacities suggests that progression to a more malignant behaving tumor occurs with time. Although not stated, the authors may have been attempting to answer this question by performing immunohistochemical analysis.
Specifically, what is there to gain from this article [4]? Careful follow-up of tumors of 2 cm or less with pure GGO radiographic features rather than surgical resection is an option. It must however be recognized in this series that two small lesions (ie, 5 mm and 7 mm with pure GGO) were adenocarcinomas. The authors attempted to measure tumor proliferative activity using immunohistochemistry. The expression of these markers was statistically different between lesions of pure GGO and those with a solid component, which supports the hypothesis that removal of tumors with solid components are necessary. However, no correlation with clinical behavior is provided. We are not entirely certain of the significance of the immunohistochemical markers used. We are also not certain of the long-term behavior of GGOs. Do they inevitably all progress to more aggressive adenocarcinoma? If so, for how long a period would this take? It seems unlikely that all GGOs progress to aggressive adenocarcinoma, because this disease would then be present in almost epidemic proportions, given the high frequency of GGOs. Our knowledge of GGOs and the behavior of BAC are as long as the history of CT scanning, which is approximately 2 decades. There is much to learn and this series has contributed in a small way. Further larger series with documentation of clinical behavior will be needed to answer questions regarding natural history, frequency of follow-up, and the role and type of intervention.
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References
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- Ebright MI, Zakowski MF, Martin J, et al. Clinical pattern and pathologic stage but not histologic features predict outcome for bronchioloalveolar carcinoma Ann Thorac Surg 2002;74(5):1640-1646.[Abstract/Free Full Text]
- Hiatt KM, Highsmith WE. Lack of DNA evidence for jaagsiekte sheep retrovirus in human bronchioloalveolar carcinoma Hum Pathol 2002;33(6):680.[Medline]
- Noguchi M, Morikawa A, Kawasaki M, et al. Small adenocarcinoma of the lung. Histologic characteristics and prognosis Cancer 1995;75(12):2844-2852.[Medline]
- Ohta Y, Shimizu Y, Kobayashi T, et al. Pathological and biological assessment of lung tumors showing ground-glass opacity Ann Thorac Surg 2006;81:1194-1198.[Abstract/Free Full Text]
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