A Simple Guide To Understanding Cancer Part 2

In Part 1, we covered the basics of what cancer is, how it develops, and the role of genetics in cancer susceptibility. In Part 2, we dive deeper into cancer diagnosis, treatment, and the exciting frontier of precision oncology — where genetic insights are transforming how cancer is detected and treated.

How Is Cancer Diagnosed?

Imaging

Imaging studies — X-ray, CT scan, MRI, PET scan, and ultrasound — are used to detect tumors, assess their size and location, and evaluate whether cancer has spread to lymph nodes or distant organs. Imaging is essential for staging — determining how advanced the cancer is — which guides treatment decisions.

Biopsy

A biopsy — removing a sample of tissue for laboratory analysis — is required for definitive cancer diagnosis. The biopsy sample is examined under a microscope (histopathology) to confirm malignancy, identify the cancer type, and assess features that predict behavior and treatment response.

Molecular and Genetic Testing of Tumors

Modern cancer diagnosis goes far beyond histopathology. Comprehensive genomic profiling of tumor tissue identifies the specific mutations driving the cancer — information that is increasingly essential for treatment selection. Key tests include:

• Next-generation sequencing (NGS) panels: Test for mutations in dozens or hundreds of cancer-relevant genes simultaneously
• Immunohistochemistry (IHC): Tests for protein expression (e.g., HER2, PD-L1, hormone receptors) that guide targeted therapy and immunotherapy selection
• FISH (Fluorescence In Situ Hybridization): Detects gene amplifications and rearrangements (e.g., HER2 amplification, ALK rearrangement)
• Liquid biopsy: Detects tumor DNA circulating in the blood — enabling non-invasive monitoring of treatment response and early detection of resistance

Cancer Treatment: The Modern Toolkit

Surgery

Surgical removal of the tumor remains the primary treatment for many solid cancers. Advances in minimally invasive and robotic surgery have reduced recovery times and improved outcomes. The extent of surgery is guided by tumor genetics — some genetic profiles indicate a higher risk of local recurrence, requiring wider margins.

Radiation Therapy

High-energy radiation damages cancer cell DNA, preventing replication. Modern techniques (IMRT, stereotactic radiosurgery) deliver radiation with high precision, minimizing damage to surrounding healthy tissue.

Chemotherapy

Cytotoxic drugs that kill rapidly dividing cells. Pharmacogenomic variants affect how chemotherapy drugs are metabolized — influencing both efficacy and toxicity. DPYD variants affect fluorouracil (5-FU) metabolism; UGT1A1 variants affect irinotecan metabolism.

Targeted Therapy

Drugs that target specific molecular drivers of cancer growth. Examples include EGFR inhibitors for EGFR-mutant lung cancer, HER2-targeted therapies for HER2-positive breast cancer, BRAF inhibitors for BRAF V600E-mutant melanoma, and PARP inhibitors for BRCA-mutant cancers. Targeted therapy requires molecular testing to identify the specific mutation being targeted.

Immunotherapy

Drugs that activate the immune system to recognize and destroy cancer cells. PD-1/PD-L1 inhibitors (pembrolizumab, nivolumab) are effective across multiple cancer types. Response is predicted by PD-L1 expression, tumor mutational burden (TMB), and microsatellite instability (MSI) status — all determined by molecular testing.

Hereditary Cancer Syndromes: Know Your Risk

Approximately 5–10% of cancers are caused by inherited mutations in cancer predisposition genes. Key hereditary cancer syndromes include:

• Hereditary Breast and Ovarian Cancer (HBOC): BRCA1/BRCA2 mutations. Significantly elevated risk of breast, ovarian, prostate, and pancreatic cancer.
• Lynch Syndrome: MLH1, MSH2, MSH6, PMS2 mutations. Elevated risk of colorectal, endometrial, ovarian, and other cancers.
• Familial Adenomatous Polyposis (FAP): APC mutations. Near-certain colorectal cancer risk without prophylactic colectomy.
• Li-Fraumeni Syndrome: TP53 mutations. Elevated risk of multiple cancer types from childhood.

FAQs

Should I get genetic testing if I have cancer?

Yes — for most cancers, tumor molecular profiling is now standard of care and guides treatment selection. Germline genetic testing (testing your inherited DNA) is recommended if you have a hereditary cancer syndrome or a family history suggesting inherited risk.

What is liquid biopsy and how is it used?

Liquid biopsy detects tumor DNA circulating in the blood. It's used to monitor treatment response, detect resistance mutations early, and — increasingly — for early cancer detection in high-risk individuals. It's less invasive than tissue biopsy and can be repeated over time to track cancer evolution.