In one line
Cancer in pregnancy is a multidisciplinary problem in which — for almost every tumour type — the mother receives stage-appropriate treatment without delay, using surgery and second/third-trimester chemotherapy to preserve the pregnancy where possible, and iatrogenic prematurity (not chemotherapy) is the dominant threat to the neonate.
This chapter assumes the diagnostic groundwork already taught at Intermediate — what an adnexal mass work-up is, how a breast lump is triaged, the basics of FIGO staging, and the SA cervical screening pathway — and spends its words on the consultant layer: how the tumour subtype and gestation together rewrite the plan, where the guidelines disagree, the named regimens and their exact differences, and the SA referral reality. The first-principles "is this malignant?" reasoning lives in the Intermediate oncology chapters and in Cervical premalignancy colposcopy.
Assessment
The diagnostic task is to overcome the physiological camouflage that delays cancer diagnosis in pregnancy (breast nodularity, anaemia, fatigue, fundal-height "masses") and then to stage accurately while protecting the fetus. Pregnancy-associated cancer occurs in roughly 1 in 1000 pregnancies (FIGO cites 17–27 per 100 000); breast, haematological (lymphoma/leukaemia), melanoma and cervical cancers dominate. Incidence is rising with later childbearing and with incidental findings from cell-free DNA aneuploidy screening — an aberrant cfDNA result with multiple chromosomal imbalances should prompt maternal whole-body MRI, not reassurance.
- Tissue first. Biopsy is safe in pregnancy; never defer histological diagnosis. A breast lump still needs core biopsy, and a persistent or suspicious adnexal mass needs the standard work-up — that groundwork is assumed here, and the screening pathway that should have caught cervical disease earlier sits in SA cervical screening.
- Imaging — radiation is rarely the problem. Below ~50–100 mGy there is no measurable deterministic fetal harm. A chest radiograph delivers 0.001–0.01 mGy and a chest CT only about 0.01–0.66 mGy (so it must not be withheld when indicated); CT abdomen/pelvis and whole-body PET/CT each deliver roughly 10–50 mGy (childhood-cancer risk 1 in 1000 to 1 in 200). MRI without gadolinium is the workhorse for staging — gadolinium crosses the placenta and is linked to rheumatological disease and neonatal death, so it is avoided. Use the lowest feasible dose for any X-ray; routine fetal or gonadal shielding is not recommended (ASCO 2025).
- Sentinel node mapping uses technetium-99m (cumulative pregnancy dose stays below 5 mGy); blue dyes are avoided (anaphylaxis) and indocyanine green is acceptable.
- Tumour markers mislead. CA-125, AFP, β-hCG, inhibin and LDH all shift in normal pregnancy — interpret only as trends, never as single-point staging tools.
- HIV. In the SA context every patient is offered/confirmed HIV testing; immunosuppression worsens cervical disease and complicates chemotherapy tolerance (see Cervical premalignancy colposcopy). Apply SA HIV Consolidated Guidelines including PVT for the neonate.
The advanced assessment
Beyond "biopsy, stage, MDT", the work is reading three variables together — tumour biology, stage, and gestation — because each combination produces a different plan, and then handling the subtle presentations and the staging traps.
Gestation is the master variable, and it interacts with everything. The same diagnosis demands a different plan at 8, 18 and 32 weeks because gestation simultaneously fixes (a) whether termination is even on the table, (b) whether chemotherapy is permissible now or must wait for organogenesis to finish, (c) whether the surgical window is open (the second trimester is the operative sweet spot), and (d) how many weeks of fetal maturity can be bought before a delivery that is, in almost every case, the real treatment-limiting step. "Treat stage-appropriately" means nothing until every decision is anchored to the precise gestation.
Severity stratification is about urgency, not just stage. Stratify the presenting problem into three tiers because the tiers drive tempo:
- Oncological emergency (leukaemic blast crisis, spinal cord compression, superior vena cava obstruction from bulky mediastinal lymphoma, airway-threatening thyroid or head-and-neck disease): treat now, on the disease's own merits — pregnancy does not buy you time and rarely changes the immediate intervention. A first-trimester acute leukaemia is the sharpest version: the maternal disease is lethal in weeks untreated, induction chemotherapy in the first trimester is genuinely teratogenic, and the honest counselling is that continuing the pregnancy and deferring induction is not safe for the mother — most experts induce promptly and counsel on the fetal risk, or offer termination.
- Aggressive but not emergent (most invasive breast cancer, high-grade lymphoma, epithelial ovarian cancer): treat without delay but with time to convene the MDT, complete staging and time chemotherapy past organogenesis.
- Indolent / surveillable (microinvasive cervical disease, low-grade or early-stage tumours, some borderline ovarian tumours): the legitimate option to watch and bridge to fetal maturity exists, and choosing it is a defensible consultant judgement — but only with a documented surveillance plan and informed maternal consent.
Subtle and atypical presentations the camouflage hides. Pregnancy-associated breast cancer is more often diagnosed at a higher stage and is more frequently triple-negative or HER2-positive — the "nodularity is normal" reflex delays it, and a discrete, dominant or enlarging mass in a lactating or pregnant breast is cancer until a core biopsy says otherwise; never settle for fine-needle aspiration cytology here, because the proliferative gestational background degrades cytological interpretation. Cervical cancer presenting as antepartum bleeding is mislabelled as a placental or "show" bleed; a speculum-and-cervix examination is mandatory for unexplained bleeding, and a friable or bulky cervix is biopsied, not just cytologically screened. An adnexal mass found on the dating scan that persists beyond ~16 weeks, is >5–6 cm, solid or with the standard malignant ultrasound morphology, is not a corpus-luteum cyst and needs IOTA/O-RADS characterisation and a surgical plan.
Where the staging tools mislead in pregnancy:
- Tumour markers are the classic trap. CA-125 peaks physiologically in the first trimester and at delivery; AFP rises throughout; β-hCG and inhibin are gestational hormones; LDH rises with haemolysis and the placenta. A single elevated value cannot stage, and a "rising" marker may simply be a maturing pregnancy. Use them only as within-patient trends after a baseline, and never to decide between continuation and termination.
- Lymph-node assessment loses fidelity as the uterus grows. Surgical pelvic lymphadenectomy in cervical cancer is feasible only up to roughly 20–22 weeks, beyond which uterine volume collapses the nodal yield and the operation becomes hazardous. PET/CT (high background uptake, fetal dose) and the gravid uterus both degrade radiological nodal staging. This is why the cervical-cancer plan hinges on gestation at diagnosis.
- Restaging imaging is constrained. Gadolinium and high-dose CT/PET are limited, so the staging you can obtain antenatally is often less complete than you would accept outside pregnancy — and the consultant judgement is to act on the best feasible staging rather than to delay treatment chasing a perfect one.
Management
Decisions run immediate → ongoing → long-term and are owned by a tumour board (oncology, gynae-oncology, MFM, neonatology, radiology, pathology, anaesthesia, psychology) — convening this MDT is the first step.
Immediate
- Confirm gestation precisely (drives every threshold) and establish maternal wishes regarding continuation versus termination — a permitted choice under the SA Choice on Termination of Pregnancy Act and central where treatment cannot proceed alongside pregnancy.
- Stabilise oncological emergencies (cord compression, SVC obstruction, leukaemic crisis) on their own merits — pregnancy does not change that calculus.
Ongoing (the operative core)
- Surgery is safe in any trimester; the second trimester is optimal for major abdominal/pelvic surgery.
- Chemotherapy is deferred past organogenesis — never in the first trimester (malformation risk ~14% single-agent, up to 25% combination), but after ~14 weeks the major-malformation rate falls to roughly background (~1.3%). Standard regimens (anthracyclines, cyclophosphamide, carboplatin + paclitaxel, cisplatin, 5-FU, vincristine) are used at full, weight-adjusted dose.
- Stop chemotherapy by ~33–35 weeks and leave a 3-week washout before delivery (1–2 weeks for weekly/fortnightly regimens) so fetal marrow and placental clearance recover — neonatal myelosuppression is the avoidable harm.
- Absolute drug exclusions: methotrexate and aminopterin (folate-antagonist embryopathy), trastuzumab/anti-HER2 (oligohydramnios, fetal death), tamoxifen (defer to postpartum), and (among the anthracyclines) idarubicin. Antimetabolites are not banned as a class — cytarabine and fluorouracil are used after the first trimester, and daunorubicin is the anthracycline of choice.
- Radiotherapy to the pelvis is contraindicated; supradiaphragmatic RT with shielding is occasionally feasible but usually deferred.