Lung Carcinoma Lecture

General Considerations of Lung Carcinoma

Lung carcinoma, which is also commonly referred to as bronchogenic carcinoma or simply lung cancer, is a malignant neoplasm that arises from the respiratory tract epithelium. It is broadly categorized into two major groups: small cell lung cancer (SCLC) and non-small cell lung cancer (NSCLC). Cigarette smoking is identified as the single largest risk factor, contributing to more than $80\%$ of all cases. While symptoms such as a cough or chest discomfort are common, many patients remain asymptomatic in the early stages, and some only present once the disease has metastasized. Hemoptysis is another symptom, though it is less common than others. Diagnosis generally begins with suspicion from a chest x-ray or CT scan and must be confirmed through a biopsy. Treatment modalities include surgical intervention, chemotherapy, and radiation therapy. Despite medical advances, the general prognosis for lung cancer remains poor, necessitating a focus on prevention and early detection.

Key Clinical Points and Histologic Subtypes

Lung cancer is histologically divided into small cell lung cancer and non-small cell lung cancer. Small cell lung cancer (SCLC) is currently staged as either limited or extensive disease. It is notable for being highly responsive to chemotherapy, with cisplatin-based regimes serving as the treatment of choice for both limited and extensive stages. In the case of limited-disease SCLC, the addition of thoracic radiotherapy has been shown to provide superior locoregional control and a significant survival benefit. Non-small cell lung cancer (NSCLC) is primarily treated with surgical resection in its early stages, specifically stages I, II, and certain stage IIIa cases. Adjuvant chemotherapy or radiotherapy appears to improve survival rates in patients with N1 and N2 nodal involvement. For locally advanced NSCLC (stages IIIa N2 and IIIb), elective treatment typically involves a combination of chemotherapy and radiotherapy, which can be administered either concomitantly or sequentially.

For metastatic NSCLC (stage IV), the prognosis is very poor. However, patients with a good performance status may see a small but significant improvement in survival and symptom relief when treated with cisplatin-based combination chemotherapy compared to best supportive care alone. Newer cytotoxic agents such as gemcitabine, vinorelbine, and paclitaxel have demonstrated effectiveness when used in combination with cisplatin or carboplatin.

Epidemiology and Environmental Risk Factors

Epidemiological data from the United States indicates that approximately $171,900$ new cases of lung carcinoma are diagnosed annually, though figures from $2007$ suggested as many as $213,380$ cases (roughly $15\%$ of all cancer diagnoses). Annual deaths reach approximately $157,200$ (or $160,390$, representing $29\%$ of all cancer deaths as of $2007$). The incidence of lung cancer is currently rising among women but appears to be leveling off among men, with the peak incidence occurring between ages $55$ and $60$. Only $2\%$ of cases occur in individuals under the age of $40$. Black men are identified as being at an especially high risk for the disease. Cigarette smoking, including passive or second-hand smoke, is the primary cause. While the risk of lung cancer declines after smoking cessation, it probably never returns to the baseline risk of a never-smoker. Other environmental and occupational risk factors include exposure to radon (radium and uranium), asbestos, silica, arsenic, chromates, nickel, chloromethyl ethers, beryllium, and coke oven emissions. The risk is significantly compounded when occupational toxin exposure is combined with cigarette smoking. Air pollution and cigar smoke contain carcinogens, though they have not been definitively shown to cause lung carcinoma on their own.

Pathophysiology and Genetic Mutations

Development of lung carcinoma requires prolonged exposure to cancer-promoting agents, leading to the accumulation of multiple genetic mutations in respiratory epithelial cells before they become neoplastic. Specific mutations contribute to the proliferation of abnormal cells, including mutations in genes that stimulate cell growth such as K-RAS and MYC, genes coding for growth factor receptors like EGFR and HER2/neu, and genes that inhibit apoptosis such as BCL-2. Additionally, mutations that inhibit tumor-suppressor genes, including P53 and APC, play a critical role. Lung carcinoma results only after a sufficient number of these genetic mutations have accumulated within the cells.

Classification and Features of Non-Small Cell Lung Carcinoma (NSCLC)

NSCLC is categorized into several types, each with distinct clinical behaviors and histological features. Epidermoid or squamous cell carcinoma is most common in men and is closely correlated with a history of smoking. While these tumors were historically seen arising centrally from segmental or subsegmental bronchi near the hilus, the incidence of peripheral squamous cell carcinoma is increasing. Histologically, these are identified as well-differentiated tumors by the presence of keratinization or intercellular bridges. Adenocarcinoma is the most common lung cancer type in women and nonsmokers, arising from glands and characterized by glandular differentiation or mucin production. These lesions are usually smaller than $4\,cm$ and located peripherally, arising from terminal bronchioles and alveoli. Adenocarcinomas grow more slowly than squamous cell carcinomas but tend to metastasize earlier and more widely. Histologically, they show a pure bronchioloalveolar growth pattern without evidence of stromal, vascular, or pleural invasion. Large cell carcinoma, or large cell anaplastic carcinoma, is an undifferentiated malignant epithelial tumor lacking the features of SCLC or glandular/squamous differentiation. It features large nuclei and a moderate amount of cytoplasm. A variant of this is large cell neuroendocrine carcinoma, which is known for early hematogenous metastasis.

Features of Small Cell Lung Carcinoma (SCLC)

Small cell carcinoma, also known as oat cell carcinoma, is a highly malignant and aggressive tumor with a distinctive cell type. It has a very strong relationship with cigarette smoking, with only $1\%$ of cases occurring in nonsmokers. These tumors can occur in the major bronchi or the lung periphery. SCLC is known for early and widespread metastasis and is considered virtually incurable. For untreated patients, the survival time is typically only $1$ to $3$ months, with half of those individuals dying within $12$ to $15$ weeks. With treatment, about $10\%$ of patients may survive to the $2$-year mark. SCLC is categorized into two stages: limited disease and extensive disease.

Signs, Symptoms, and Clinical Presentation

Approximately $25\%$ of lung cancer patients are asymptomatic, and their tumors are discovered via chest imaging. Symptoms generally arise from local tumor growth, regional spread, or distant metastasis. Local symptoms include a cough in $80\%$ of cases, sputum production (expectoration), chest pain in $40\%$ of cases, weight loss in $40\%$ of cases, and dyspnea in $60\%$ of cases (often due to airway obstruction). Less common symptoms include hemoptysis, dysphonia (caused by invasion of the left recurrent nerve), fatigue, and fever. Infectious respiratory syndromes may arise, such as bronchopneumonia, pneumonia, or post-obstructive abscesses, the latter of which may require bronchoscopy for diagnosis.

Locoregional invasion can lead to specific syndromes. Mediastinal syndrome includes Superior Vena Cava (SVC) Syndrome, which presents with headaches, a sensation of head fullness, facial or upper extremity swelling, facial and truncal plethora (flushing), and supine breathlessness. Physical signs include edema of the face and upper extremities, along with dilated neck and subcutaneous veins. SVC syndrome is more common in SCLC. Pancoast's Syndrome occurs with apical tumors (usually NSCLC) that invade the brachial plexus, pleura, or ribs, resulting in shoulder and upper extremity pain and atrophy of the ipsilateral hand. Horner's Syndrome (ptosis, miosis, enophthalmos, and anhidrosis) occurs when the cervical stellate ganglion or paravartebral sympathetic chain is involved.

Metastatic Spread and Paraneoplastic Syndromes

Metastasis can affect various organ systems with diverse presentations. Spread to the pericardium may be asymptomatic or lead to cardiac tamponade or constrictive pericarditis. Esophageal compression leads to dysphagia. Liver metastasis results in gastrointestinal symptoms and eventually hepatic insufficiency. Brain metastasis causes behavioral changes, confusion, aphasia, seizures, paralysis, nausea, vomiting, and potentially coma or death. Bone metastasis is characterized by severe pain and pathologic fractures. While the adrenal glands are a common site for metastasis, they rarely lead to adrenal insufficiency.

Paraneoplastic syndromes are conditions not caused directly by cancer cell invasion. These include hypercalcemia (due to tumor production of parathyroid hormone-related protein), Syndrome of Inappropriate Antidiuretic Hormone secretion (SIADH), finger clubbing (with or without hypertrophic osteoarthropathy), Trousseau's syndrome (hypercoagulability with migratory superficial thrombophlebitis), and Eaton-Lambert syndrome (myasthenia). Neurologic syndromes may also occur, including neuropathies, encephalopathies, encephalitides, myelopathies, and cerebellar disease.

Diagnostic Protocols and Imaging

The initial diagnostic test is a chest x-ray, which may reveal a single mass, multifocal masses, or a solitary pulmonary nodule. Subtle changes include an enlarged hilum, widened mediastinum, tracheobronchial narrowing, atelectasis, nonresolving parenchymal infiltrates, cavitary lesions, or unexplained pleural thickening/effusion. These findings require follow-up with high-resolution CT (HRCT) and cytopathologic confirmation. CT scans are used to demonstrate characteristic patterns and guide needle biopsies. Bronchoscopy is the procedure of choice for obtaining tissue as it is the least invasive. A combination of washing, brushing, and fine-needle aspiration (FNA) of visible endobronchial lesions or lymph nodes (paratracheal, subcarinal, mediastinal, or hilar) yields a diagnosis in $90$ to $100\%$ of cases. Mediastinoscopy is a higher-risk procedure used before surgery to evaluate enlarged mediastinal lymph nodes. Other diagnostic tools include thoracotomy or video-assisted lung biopsy, echography for detecting metastasis, and PET scanning to identify malignant mediastinal nodes and distant metastases.

International Staging System for Lung Cancer (TNM)

The staging of lung cancer is based on the Primary Tumor (T), Regional Lymph Nodes (N), and Distant Metastasis (M). The T categories reflect tumor size and extent: TX (primary tumor cannot be assessed), T0 (no evidence of primary tumor), Tis (carcinoma in situ), T1 (tumor $\leq 3\,cm$), T1a(mi) (minimally invasive), T1a ($\leq 1\,cm$), T1b ($> 1$ to $\leq 2\,cm$), T1c ($> 2$ to $\leq 3\,cm$), T2 (tumor $> 3$ to $\leq 5\,cm$), T2a (tumor $> 3$ to $\leq 4\,cm$), T2b (tumor $> 4$ to $\leq 5\,cm$), T3 (tumor $> 5$ to $\leq 7\,cm$), and T4 (tumor $> 7\,cm$).

Regional Lymph Nodes (N) are categorized as N0 (no regional lymph node metastasis), N1 (metastasis to ipsilateral peribronchial/hilar nodes or intrapulmonary nodes by direct extension), N2 (metastasis to ipsilateral mediastinal or subcarinal nodes), and N3 (metastasis to contralateral mediastinal, contralateral hilar, scalene, or supraclavicular nodes).

Distant Metastasis (M) includes M0 (no distant metastasis), M1 (distant metastasis present), M1a (separate tumor nodules in a contralateral lobe or pleural/pericardial nodules/effusion), M1b (single extrathoracic metastasis), and M1c (multiple extrathoracic metastases in one or more organs).

Stage Grouping combines these factors: Stage 0 (Tis N0 M0), Stage IA1 (T1a(mi) N0 M0), Stage IA2 (T1b N0 M0), Stage IA3 (T1c N0 M0), Stage IB (T2a N0 M0), Stage IIA (T2b N0 M0), Stage IIB (T1a-c N1 M0, T2a-b N1 M0, or T3 N0 M0), Stage IIIA (T1-T2 N2 M0, T3 N1 M0, T4 N0-1 M0), Stage IIIB (T1-T2 N3 M0, T3-T4 N2 M0), Stage IIIC (T3-T4 N3 M0), Stage IVA (any T any N M1a-b), and Stage IVB (any T any N M1c).

Prognosis

The prognosis for lung cancer is generally poor. Untreated patients with advanced NSCLC have a median survival of $6$ months, which increases to about $9$ months with treatment. For SCLC, the extensive-stage 5-year survival rate is less than $1\%$. Limited-stage SCLC has a median survival of $20$ months and a 5-year survival rate of $20\%$. For NSCLC, the 5-year survival varies greatly by stage, from $60$ to $70\%$ for stage I patients to virtually $0\%$ for stage IV patients.

Treatment Strategies for SCLC and NSCLC

Treatment choices depend on tumor type and stage. Surgery is only performed on patients with adequate pulmonary reserve; a preoperative FEV1 $> 2\,L$ is generally required for pneumonectomy. SCLC is initially responsive to treatment, but responses are short-lived. Surgery is rarely used for SCLC unless the tumor is a small, focal solitary pulmonary nodule. In limited-disease SCLC, the most effective treatment is a combination of etoposide and a platinum compound (cisplatin or carboplatin) for $4$ to $6$ cycles. Radiation improves response in limited-stage SCLC. Prophylactic cranial irradiation is often advocated because chemotherapy does not cross the blood-brain barrier. In extensive-stage SCLC, treatment is similar but excludes concurrent radiation. Survival in extensive-stage disease may be improved by replacing etoposide with topoisomerase inhibitors like irinotecan or topotecan. Recurrent SCLC has a very poor prognosis.

For NSCLC, treatment also follows the stage. Stage I and II are treated with surgical resection (lobectomy or pneumonectomy) and lymph node sampling. Smaller resections like segmentectomy are using for those with poor reserve. Surgery cure rates are $55-75\%$ for stage I and $35-55\%$ for stage II. Adjuvant chemotherapy (specifically cisplatin plus vinorelbine) is often helpful for stages Ib and II, although the survival improvement is small (a 5-year survival of $69\%$ vs $54\%$). Stage III represents locally advanced disease. Stage IIIA discovered at surgery has a $20-25\%$ 5-year survival rate. Clinically staged IIIA is usually treated with radiation and chemo, though the median survival is poor ($10-14$ months). Stage IIIB patients are offered radiation, chemotherapy, or both. The 5-year survival for stage IV is less than $25\%$ at one year, and the goal is palliation using chemotherapy and radiation to reduce tumor burden and symptoms.

Complications and Symptom Management

Malignant pleural effusions are initially treated with thoracentesis. Recurrent symptomatic effusions are managed via a chest tube and pleurodesis, often using $6$ to $8\,g$ of talc (or tetracycline/bleomycin) to scar and eliminate the pleural space, which is effective in over $90\%$ of cases. SVC syndrome is treated with chemotherapy for SCLC or radiation for NSCLC; corticosteroids are common but unproven. Apical tumors are treated with surgery and potentially preoperative or adjuvant radiation and chemotherapy. Palliative procedures for stage IV disease include thoracentesis, pleurodesis, placement of drainage catheters, bronchoscopic fulguration, stenting for airway occlusion, and spinal stabilization for impending cord compression.