LUNG CANCER – EARLY DIAGNOSIS BY COMPUTED TOMOGRAPHY

Luciano Sabolla MD

Lung cancer is the most common malignant tumour in men and the second most frequent in women, after breast cancer.  Overall it accounts for 13% of all malignant cancer cases.

Thanks to the various oncologic therapies, survival at 5 years after diagnosis has improved in all European countries from 8% to 13%, but is still too low.

This encourages doctors to look for new possibilities of early detection of lung cancer, i.e. for new effective secondary prevention tools (primary prevention is pursued by abolishing the habit of smoking and eliminating environmental carcinogens).

To this end numerous trials have been carried out around the world to test the usefulness of chest computed tomography (CT) without contrast medium (baseline CT) at low radiation doses (LDCT).

The scientific observations carried out for years on thousands of volunteers undergoing LDCT show that it is reasonable to expect an advantage in subjects at least 50 years of age who have smoked an average of at least 20 cigarettes a day for 20 years (≥ 20 pack-year), if they are still smokers or if they have quit smoking for less than 15 years.

The numerous observations available, although partially contradictory, allow us to consider LDCT as the most effective means of screening for lung cancer in individuals at risk nowadays.

LDCT is the method with the highest capacity to identify a micronodule in the pulmonary parenchyma, thanks to the great difference in density between the tissue of the nodule and the air contained in the alveoli surrounding it (CT is in fact a tomodensitometric methodical).

CT is able to establish the heteroformative nature of a micronodule on a morphological basis, i.e. recognizing certain characteristics of its contours, on a structural basis by establishing the absence of calcifications in its context (calcification lay for a benign form) and evaluating its dimensional evolution through the repetition of the scan anually, since the dimensional stability of a pulmonary nodule for a period longer than two years is strongly associated with a benign nature.

It is now accepted that LDCT allows the detection of lung cancer in almost 7% of subjects at risk, enrolled according to the above requirements, if they are checked once a year for ten years.

This rate, however, corresponds to about half of the lung cancers actually present in the population at risk, being identifiable by CT only the neoplasms occurring in the lung parenchyma.

The basal thoracic CT scan misses many of the fast-growing peripheral neoplasms, which account for 15% to 18% of all lung cancers, i.e. the most aggressive forms (those with a “small cell” histotype).

The basal CT scan fails to demonstrate the “central” tumours too, occurring in the mucous membrane of the large bronchi, forms which can only be detected through bronchoscopic procedures.

On the other hand, the cases identified by LDCT are almost always revealed in a favourable phase, compared to patients diagnosed at the onset of symptoms, i.e. at Stage I or II, when the maximum surgical indication (high resectability) and probability of complete recovery after 5 years from surgical exeresis are given.

One of the most important oncological institutions in Lombardy, investigating thousands of (ex)smokers by LDCT once a year for 10 years, has identified malignant pulmonary neoplasms in about 7% of volunteers enrolled. The detection rate in the first two years was 1.1% person-years. These neoplasms were operable in 86% of cases and were removed without operative mortality.

The National Lung Screening Trial in the USA showed a 7% reduction in total lung cancer mortality among individuals undergoing LDCT once a year, compared to the arm undergoing chest radiography.

In one case study, LDCT screening increased the survival of lung cancer subjects by 9 years compared to patients diagnosed on a clinical basis only.

The most important problem for those who undergo LDCT is the anxiety when is detected “a nodule” of an unspecified nature. Benign nodules in the lung are found at LDCT in about half of the subjects examined; to further investigations they prove to be benign in 98% of cases, but with a considerable economic and health commitment and in any case after having induced important psychological consequences.

Distress generated by the LDCT screening produces however the positive effect of convincing the current smokers to definitively stop smoking, in 14% of the cases, against 5% of oncologic patients not submitted to LDCT.

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