(a) Describe the molecular mechanisms of carcinogenesis of breast carcinoma. Describe the salient histopathological features of…

Molecular mechanisms and histopathology of breast carcinoma. Breast carcinoma arises through a multistep sequence in which normal mammary epithelium acquires genetic and epigenetic alterations that allow clonal expansion, invasion and metastasis. In hereditary and high-risk forms, biallelic inactivation of BRCA1 or BRCA2 impairs homologous recombination repair of DNA double-strand breaks, producing genomic instability and increasing susceptibility to further mutations. TP53 mutations remove the principal cell-cycle checkpoint and apoptosis safeguard, allowing survival of damaged cells. Growth signalling is amplified by HER2/neu overexpression or amplification, which drives proliferation, survival and angiogenesis, while oestrogen receptor and progesterone receptor signalling in hormone-sensitive tumours promotes clonal expansion and is the basis of endocrine therapy. The molecular events explain why tumours are classified by ER, PR and HER2 status. Invasive carcinoma of no special type, formerly invasive ductal carcinoma, is the commonest type. It shows irregular nests, cords, angulated glands and single cells infiltrating a dense desmoplastic stroma with fibroblasts and inflammatory cells. The Nottingham grade is based on tubule formation, nuclear pleomorphism and mitotic count: well-formed tubules, uniform nuclei and low mitoses indicate grade I, whereas poor tubule formation, marked pleomorphism and high mitoses indicate grade III. Tubule formation is assessed as the proportion of tumour forming gland-like structures, and mitoses are counted in high-power fields. Lymphovascular invasion, central necrosis and a brisk stromal reaction are adverse features.

IgA structure and disease role. The diagram would show a secretory IgA dimer: two IgA monomers, each with two α heavy chains and two light chains linked by disulfide bonds, joined by a J chain; the dimer is bound to secretory component derived from polymeric immunoglobulin receptor, which protects it from proteolysis. The J chain is essential for dimer formation and transport. Serum IgA is mainly monomeric, while secretory IgA is dimeric and is the principal immunoglobulin of mucosal secretions. It neutralises pathogens, prevents adherence to epithelium and limits mucosal invasion. Clinically, selective IgA deficiency predisposes to recurrent sinopulmonary and gastrointestinal infections and is associated with celiac disease and autoimmune disease; IgA nephropathy, or Berger disease, is caused by deposition of IgA-containing immune complexes in the mesangium and may present with haematuria.

Opportunistic infections in AIDS. Opportunistic infections are caused by organisms that are usually harmless but produce disease when host immunity, especially cell-mediated immunity, is impaired. In AIDS, defined by marked CD4 T-cell depletion or AIDS-defining illness, bacterial infections include Mycobacterium tuberculosis and Mycobacterium avium complex; parasitic infections include Toxoplasma gondii and Cryptosporidium species; viral infections include cytomegalovirus, herpes simplex virus, varicella-zoster virus and JC virus; fungal infections include Candida species, Cryptococcus neoformans, Histoplasma capsulatum and Pneumocystis jirovecii. Pneumocystis jirovecii pneumonia is a classic AIDS-defining fungal infection. The spectrum reflects loss of CD4 T-cell help, impaired mucosal immunity and defective macrophage activation. These infections are more frequent at low CD4 counts and are reduced by antiretroviral therapy.

ARBs, ACE inhibitors and hypertensive emergency. ARBs are selective AT1 receptor blockers such as losartan, valsartan and telmisartan; they prevent angiotensin II from binding AT1 receptors, reducing vasoconstriction, aldosterone secretion, sodium retention and cardiac remodelling. ARBs and ACE inhibitors both lower blood pressure by reducing angiotensin II effects, but ARBs act downstream of the enzyme. Unlike ACE inhibitors, which block conversion of angiotensin I to angiotensin II and also reduce bradykinin degradation, ARBs do not cause bradykinin accumulation and therefore have less cough and angioedema; they also do not affect bradykinin B2 receptor-mediated effects. In hypertensive emergency, severe hypertension with acute end-organ damage requires ICU monitoring and titratable IV therapy. Labetalol, esmolol, nitroprusside or nicardipine are used; sublingual nifedipine is avoided because of unpredictable precipitous falls. The general target is to reduce mean arterial pressure by no more than 25% in the first hour, then gradually to about 160/100 mmHg over 2–6 hours, with special targets for aortic dissection, acute stroke or eclampsia.

Granulomatous inflammation. Granulomatous inflammation is a form of chronic inflammation in which activated macrophages transform into epithelioid histiocytes and may fuse into multinucleated giant cells, forming a granuloma. It is usually a Th1-mediated response: antigen-presenting cells release IL-12, T cells produce IFN-γ, and TNF-α sustains macrophage activation. The granuloma is often walled off by lymphocytes, limiting spread of the offending agent. Caseating granulomas have central necrosis, whereas non-caseating granulomas lack it. Types include infectious granulomas, such as caseating tuberculous granulomas, leprosy, syphilis and fungal infections; foreign-body granulomas, formed around suture, silica, talc or other indigestible material; sarcoidosis, with non-caseating granulomas in lungs and lymph nodes; Crohn's disease, with transmural non-caseating granulomas; and granulomatosis with polyangiitis (Wegener's), with necrotising granulomatous vasculitis of the upper and lower respiratory tract and kidneys. In India, tuberculosis is an important cause of caseating granulomas.

Firearm and entry-wound features. A firearm is a weapon that uses the explosive force of a propellant charge to propel a projectile through a barrel. Entry-wound features help determine range and direction. In contact wounds, the muzzle is pressed to the skin, producing a stellate laceration, muzzle imprint, soot or gunpowder in the wound and sometimes no abrasion collar. In close-range wounds, generally within about 1 metre, there is an abrasion collar or grease collar, soot impregnation and tattooing from unburnt powder particles, but no stellate laceration. In distant wounds, the entry is a clean, round or oval wound with an abrasion collar and no soot or tattooing. Soot and tattooing fade as range increases, while the abrasion collar persists at all ranges. Direction of fire is inferred from the inverted/converted wound shape, the abrasion collar, the trajectory of the projectile and, in bone, beveling: the entry bevel is inward, concave toward the direction of travel, while the exit bevel is outward. In soft tissue, entry wounds are usually smaller and may show inwardly turned edges, whereas exit wounds are larger and everted. Together these features distinguish entry from exit and estimate the distance from muzzle to target. Overall, these mechanisms, structures, infections, pharmacological actions, lesions and wound features form a coherent descriptive account.