Natural History
The natural history of Lung cancercan be described by breaking down its course
of existence into a sequence of a few simple phases based on the way we experience the
disease clinically.
- Pre-Detectable
- Carcinoma of the lung always passes through a pre-detectable phase, beginning
with its biological onset (the development of the first frankly malignant cell) and
beginning when the disease may first be shown to exist whether through sputum cytology or
chest radiography. It has been claimed that by the time a tumor is 10 mm in diameter it
has already doubled in size 30 times, contains at least one billion cells, and has
completed three-fourths of its anticipated existence. It is likely that during the
majority of a lung tumor's existence it will be undetectable by any currently available
diagnostic technique.
- Detectable-Asymptomatic
- Most cases of lung carcinoma are felt to enter a phase in which presence of the
disease is potentially demonstrable, yet continues to be without symptoms. The disease is
detectable if:
The tumor is radiographically evident (5-10 mm in diameter), or
Sputum is positive for malignant cells.
The duration of this "presymptomstic-detectable" phase is heavily
dependent on the cell type involved and on location of the primary tumor. Sputum cytology
can be positive for several years before symptoms occur in a progress from undetectable to
unresectable within a few short months. Unfortunately, only about 5% of lung cancer
diagnoses are made in this phase. These findings are typically made through incidental
X-Ray findings during workup of an unrelated condition of through sputum and X-Ray
screening of high-risk patients.
- Symptomatic Phase
- About 95% of all lung cancer diagnoses are made during the phase when the disease
has become symptomatic. Carcinoma discovered at this point in its natural history is
almost always well advanced. With very few but significant exceptions, symptomatic lung
cancer carries poor prognosis. This is because the vast majority of symptoms in this
disease are caused by either locally unresectable or metastatic tumor.