GASTRIC ADENOCARCINOMA: ANATOMY, STAGING, AND TREATMENT

-- ALL -- General Surgery Gynecology Robotic Surgery Urology WLH

General Surgery / Mar 9th, 2026 3:56 pm A⁺ | a^-

BASIC INFORMATION:

Date & Time: 09 March 2026, 20:42 IST

Lecture Handout Prepared from the Teaching Session by: Dr. R. K. Mishra

SUMMARY:

This lecture provides a structured, clinically oriented overview of gastric adenocarcinoma tailored for postgraduate surgeons and gynecologists. It begins with essential anatomy of the stomach, lymphatic drainage, and the peritoneal compartment to frame patterns of spread. The principal risk factors are outlined, with emphasis on Helicobacter pylori as the predominant modifiable risk in the United States. Diagnostic pathways focus on endoscopic biopsy as the standard, with attention to histologic differentials that must be excluded before applying adenocarcinoma-specific management. Staging relies on contrast-enhanced CT, PET limitations for peritoneal disease, and the role of endoscopic ultrasound (EUS) for T and nodal assessment. The lecture underscores the utility of staging laparoscopy when imaging or EUS suggests higher-risk local disease, primarily to avoid nonbeneficial laparotomy in the presence of peritoneal metastasis. Surgical management contrasts D1 and D2 lymphadenectomy, highlighting oncologic rationale, prognostic value, and patient selection. Treatment algorithms for resectable disease prioritize perioperative chemotherapy (commonly FLOT) with surgery in between; very early lesions may be amenable to endoscopic resection. Postoperative adjuvant choices depend on the extent of lymphadenectomy and margin status. For metastatic disease, systemic therapy is central, with biomarker-driven additions (e.g., HER2, MSI, PD-1/CPS, TMB, CLDN18.2, RET, BRAF) informing targeted and immunotherapy options. Chemotherapy backbones (FLOT, FOLFOX, CAPOX, FOLFIRI) and their key toxicities are reviewed to support clinical decision-making, toxicity surveillance, and patient counseling.

KEY KNOWLEDGE POINTS:

Gastric adenocarcinoma spreads through the gastric wall to regional lymph nodes and commonly seeds the peritoneum.
H. pylori is the principal risk factor; tobacco, smoked foods, and gastric atrophy/pernicious anemia also contribute.
Endoscopic biopsy confirms diagnosis; alternative primaries (lymphoma, neuroendocrine tumor, GIST) must be excluded.
Staging: CT chest/abdomen/pelvis with contrast is standard; PET has limited sensitivity for peritoneal metastasis; EUS assists T and N assessment.
Staging laparoscopy is indicated in seemingly advanced locoregional disease to detect occult peritoneal metastasis and avoid nonbeneficial laparotomy.
Surgery remains the cornerstone for cure; D2 lymphadenectomy provides improved oncologic clearance in suitable candidates.
Perioperative chemotherapy (commonly FLOT) improves outcomes in resectable disease not suitable for endoscopic resection.
Postoperative therapy is tailored: after D1, chemoradiation is often considered; after D2, adjuvant chemotherapy alone is typical.
Positive margins warrant combined chemoradiation in many cases.
Metastatic disease is treated with systemic therapy; biomarker testing directs targeted and immune-based additions.
Oxaliplatin-related cold neuropathy and irinotecan-related diarrhea are key regimen-specific toxicities.

INTRODUCTION:

Gastric adenocarcinoma remains a significant oncologic challenge due to its propensity for early transmural invasion, regional nodal spread, and peritoneal dissemination. Precise anatomical understanding, accurate staging, and rational integration of surgery, systemic therapy, and radiation are critical to optimize outcomes. Surgeons must be adept at selecting candidates for curative resection, defining appropriate lymphadenectomy extent, and coordinating perioperative systemic therapy. Recognizing the limitations of imaging for peritoneal disease and applying staging laparoscopy judiciously are pivotal to avoid futile operations in advanced disease.

LEARNING OBJECTIVES:

Describe gastric and peritoneal anatomy pertinent to tumor spread and lymphadenectomy.
Outline evidence-based staging pathways, including the roles and limitations of CT, PET, EUS, and staging laparoscopy.
Formulate treatment strategies for early, locally advanced, and metastatic gastric adenocarcinoma, including perioperative chemotherapy choices, surgical extent, and adjuvant therapy tailoring.

CORE CONTENT:

Gastric and Peritoneal Anatomy in Oncologic Context

1.1. Gastrointestinal Continuity
- Esophagus transitions to the stomach; distal outflow to the duodenum and small intestine; continuity to colon (ascending, transverse, descending, sigmoid) and rectum.
1.2. Stomach Subsites and Curvatures
- Fundus, body, pylorus; lesser and greater curvatures define primary nodal basins.
1.3. Peritoneal Compartment
- The peritoneum lies between and around visceral organs; a frequent site for transcoelomic spread and implantation in gastric cancer.
1.4. Nodal Geography
- Perigastric lymph nodes along the lesser and greater curvatures, and second-tier stations (e.g., celiac, gastrohepatic, splenic) reflect stepwise dissemination.
Etiology and Risk Factors

2.1. Predominant Risk
- Helicobacter pylori infection is the principal risk factor and should be treated when present.
2.2. Additional Risks
- Tobacco use, smoked food intake, gastric atrophy/pernicious anemia (B12 deficiency) increase risk.
2.3. Idiopathic Occurrence
- A subset develops cancer without identifiable risk factors.
Diagnosis and Histology

3.1. Diagnostic Pathways
- Upper endoscopy with direct visualization and biopsy is the most common diagnostic route.
- Cross-sectional imaging (CT/MRI) may incidentally detect gastric masses and suggest metastatic sites; biopsy of accessible metastatic lesions can establish diagnosis.
3.2. Histologic Spectrum
- Adenocarcinoma is most common and the focus of these management principles.
- Important differentials to exclude: gastric lymphoma, neuroendocrine tumors, and gastrointestinal stromal tumor (GIST).
Staging Strategy

4.1. Cross-sectional Imaging
- CT chest/abdomen/pelvis with intravenous contrast is standard and provides comprehensive anatomic staging.
4.2. PET Considerations
- PET can detect metabolically active disease but is not reliable for peritoneal metastasis; a normal PET does not exclude peritoneal spread.
4.3. Endoscopic Ultrasound (EUS)
- Assesses depth of invasion (T stage) across gastric wall layers and evaluates regional nodes.
- Advanced T stage and/or nodal involvement correlates with a substantial risk (up to approximately one-third) of occult peritoneal metastasis.
4.4. Staging Laparoscopy
- Indicated when imaging or EUS suggests locally advanced disease or nodal involvement.
- Direct inspection and sampling of the peritoneum aim to avoid noncurative laparotomy when peritoneal metastasis exists.
4.5. Clinical Staging Framework
- Stage I–III: localized/locally advanced without distant metastasis.
- Stage IV: metastatic disease (e.g., peritoneal or distant organ involvement).
Surgical Management

5.1. Central Role of Surgery
- Surgery is the primary curative modality for resectable gastric adenocarcinoma.
5.2. Lymphadenectomy Extent
- D1 Resection: Gastrectomy with perigastric lymph node dissection along lesser and greater curvatures.
- D2 Resection: D1 plus extended nodal dissection including second-tier stations (e.g., celiac, gastrohepatic, splenic).
- Oncologic Rationale: Broader nodal clearance improves staging accuracy and may reduce recurrence risk; candidates must be physiologically fit for D2.
5.3. Patient Selection
- Preference for D2 in fit patients; D1 may be chosen in older or frail individuals or where operative risk is prohibitive.
Treatment Algorithms by Stage

6.1. Very Early Disease
- Endoscopic resection may be appropriate for tiny, superficial lesions detected on endoscopy and meeting endoscopic resection criteria.
6.2. Resectable, Not Extremely Early
- Perioperative systemic therapy is standard: preoperative chemotherapy, surgical resection, followed by postoperative chemotherapy.
- FLOT is a commonly used perioperative regimen; alternatives may be selected based on tolerance and comorbidity.
6.3. Postoperative Adjuvant Considerations
- Following D1 or less: adjuvant chemotherapy with consideration of radiation therapy is common practice in many settings.
- Following D2: adjuvant chemotherapy alone is typical.
6.4. Margin and Nodal Pathology
- Negative (R0) margins are essential; positive margins (R1) often prompt combined chemoradiation.
- Nodal involvement confers higher recurrence risk and informs adjuvant intensity.
6.5. Metastatic (Stage IV) Disease
- Avoid major gastrectomy unless for palliation of complications.
- Systemic therapy is the mainstay, guided by histology and biomarkers.
Biomarker-Directed Therapy in Advanced Disease

7.1. Biomarker Testing
- Assess tumor for HER2, microsatellite instability (MSI), PD-1 combined positive score (CPS), tumor mutational burden (TMB), and other targets such as RET, BRAF, CLDN18.2.
7.2. Therapeutic Implications
- HER2-positive: add anti-HER2 therapy (e.g., trastuzumab) to chemotherapy.
- MSI-high or high PD-1/CPS/TMB: immunotherapy addition is favored due to higher likelihood of response.
- Other actionable alterations: consider targeted approaches where appropriate.
7.3. Principle of Selection
- Use targeted or immune agents only when the corresponding biomarker is present to avoid ineffective toxicity.
Systemic Chemotherapy Regimens and Toxicity Profiles

8.1. FLOT (5-FU, leucovorin, oxaliplatin, docetaxel)
- Potent regimen; key toxicities include oxaliplatin-related cold-sensitive and cumulative neuropathy, fatigue, myelosuppression, alopecia (docetaxel), gastrointestinal toxicity, and occasional ocular effects.
8.2. FOLFOX (5-FU, leucovorin, oxaliplatin)
- Similar efficacy backbone without docetaxel; neuropathy remains prominent, with generally less alopecia and myelosuppression than FLOT.
8.3. CAPOX (capecitabine, oxaliplatin)
- Oral fluoropyrimidine alternative; toxicities include neuropathy, gastrointestinal disturbances, myelosuppression, and hand–foot syndrome (palmar–plantar erythrodysesthesia).
8.4. FOLFIRI (5-FU, leucovorin, irinotecan)
- Option in metastatic settings; hallmark toxicity is irinotecan-induced diarrhea, with other fluoropyrimidine-related adverse effects.

SURGICAL PEARLS:

Thorough preoperative staging, including selective staging laparoscopy, prevents futile laparotomy when peritoneal metastasis is present.
Aim for R0 resection; document margin status meticulously.
Choose D2 lymphadenectomy in physiologically fit patients at experienced centers to enhance oncologic clearance.
Correlate nodal yield and involvement with adjuvant planning; higher nodal burden suggests greater recurrence risk.
Coordinate perioperative chemotherapy timing to optimize performance status and wound healing.

ANESTHETIC AND PHYSIOLOGICAL CONSIDERATIONS:

Not specifically discussed in the lecture.

COMPLICATIONS AND THEIR MANAGEMENT:

Intraoperative: Not specifically discussed in the lecture.
Early postoperative: Not specifically discussed in the lecture.
Late postoperative: Not specifically discussed in the lecture.

MEDICOLEGAL AND PATIENT SELECTION CONSIDERATIONS:

Confirm histology as adenocarcinoma before applying adenocarcinoma-specific pathways; exclude lymphoma, NET, or GIST.
Document comprehensive staging including the limitations of PET for peritoneal disease; justify staging laparoscopy when indicated.
Discuss and document informed consent regarding D1 vs D2 extent, anticipated benefits, and risks based on patient fitness.
Record margin and lymph node status to guide adjuvant therapy decisions.
Ensure biomarker testing in metastatic disease to align therapies with demonstrated targets and avoid nonbeneficial toxicity.

SUMMARY AND TAKE-HOME MESSAGES:

Understand peritoneal and nodal pathways of spread; anatomy guides staging and surgery.
CT with contrast is foundational; PET cannot exclude peritoneal disease—use staging laparoscopy selectively.
Surgery is central for cure; prefer D2 lymphadenectomy in fit patients, aiming for R0 margins.
Perioperative chemotherapy is standard for most resectable cases; very early lesions may be endoscopically resected.
In metastatic disease, prioritize systemic therapy and tailor with biomarker-directed agents; avoid nonbeneficial major surgery.

MULTIPLE CHOICE QUESTIONS (MCQs):

Which anatomical compartment is a frequent site of gastric adenocarcinoma metastasis and is poorly assessed by PET?

A. Mediastinum

B. Retroperitoneum

C. Peritoneum

D. Pleural space

Correct answer: C
The most common histology of primary gastric cancer discussed in this lecture is:

A. Lymphoma

B. Neuroendocrine tumor

C. GIST

D. Adenocarcinoma

Correct answer: D
The primary diagnostic test for confirming gastric cancer is:

A. PET scan

B. Upper endoscopy with biopsy

C. Serum tumor markers

D. Diagnostic laparoscopy alone

Correct answer: B
The principal modifiable risk factor for gastric cancer in the United States is:

A. EBV infection

B. H. pylori infection

C. Alcohol consumption

D. Obesity

Correct answer: B
The lymph nodes removed in a D1 resection are primarily located:

A. Along the celiac axis only

B. Along the greater and lesser curvatures

C. At the porta hepatis only

D. In the para-aortic region

Correct answer: B
Compared with D1, D2 resection includes additional lymph node dissection in:

A. Only the mesocolon

B. Celiac, gastrohepatic, and splenic regions

C. Mediastinal stations

D. Retrocrural space

Correct answer: B
The main reason to perform staging laparoscopy in seemingly advanced locoregional gastric cancer is to:

A. Obtain larger tissue biopsies

B. Assess peritoneal surfaces for occult metastasis

C. Reduce operative time of gastrectomy

D. Deliver intraperitoneal chemotherapy

Correct answer: B
A negative surgical margin after gastrectomy indicates:

A. Residual microscopic tumor is present

B. No tumor at the resection edge

C. Only nodal disease was removed

D. PET scan is unnecessary

Correct answer: B
For a very small, superficial gastric lesion identified on endoscopy, an appropriate initial management may be:

A. Primary total gastrectomy

B. Endoscopic resection

C. Neoadjuvant radiation alone

D. Observation only

Correct answer: B
The commonly used perioperative regimen cited in the lecture for resectable gastric cancer is:

A. CHOP

B. FLOT

C. BEP

D. ABVD

Correct answer: B
A characteristic toxicity of oxaliplatin is:

A. Hemorrhagic cystitis

B. Cold-sensitive peripheral neuropathy

C. Ototoxicity

D. Cardiotoxicity

Correct answer: B
Compared with FLOT, FOLFOX generally causes:

A. More alopecia

B. Less myelosuppression and alopecia

C. More ocular toxicity

D. Greater risk of mucositis only

Correct answer: B
The hallmark adverse effect of irinotecan in FOLFIRI is:

A. Nephrotoxicity

B. Diarrhea

C. Photosensitivity

D. Hypothyroidism

Correct answer: B
Hand–foot syndrome is most often associated with:

A. Docetaxel

B. Irinotecan

C. Capecitabine

D. Leucovorin

Correct answer: C
In a patient found to be HER2-positive with metastatic gastric adenocarcinoma, an appropriate addition to chemotherapy is:

A. Rituximab

B. Trastuzumab

C. Bevacizumab

D. Cetuximab

Correct answer: B
A key limitation of PET in gastric cancer staging is:

A. Lack of detection of hepatic lesions

B. Poor sensitivity for peritoneal metastases

C. Inability to detect bone metastases

D. High false positives in lung parenchyma

Correct answer: B
In the presence of peritoneal metastasis, the recommended approach to the primary gastric tumor is generally to:

A. Proceed with curative gastrectomy

B. Perform D2 dissection urgently

C. Avoid major surgery and use systemic therapy

D. Offer neoadjuvant radiation alone

Correct answer: C
After a D1 resection, many clinicians commonly consider:

A. No further therapy

B. Adjuvant chemoradiation

C. Targeted therapy only

D. Immunotherapy only

Correct answer: B
Biomarker testing in metastatic gastric cancer should be performed to:

A. Determine the need for gastrectomy

B. Identify actionable targets for therapy selection

C. Replace histologic confirmation

D. Avoid chemotherapy altogether

Correct answer: B
Positive (involved) resection margins after gastrectomy commonly lead to consideration of:

A. Observation alone

B. Additional chemotherapy and radiation

C. PET-only surveillance

D. Immediate reoperation in all cases

Correct answer: B

MOTIVATIONAL MESSAGE FROM DR. R. K. MISHRA:

“In surgery, clarity of anatomy and discipline of decision-making save more lives than speed of the knife.”

Wishing each of you steady hands, focused minds, and unwavering commitment to patient safety as you refine your craft. Continue to learn, question, and lead with humility and precision.